原子力显微镜在二维材料力学性能测试中的应用综述

REVIEW OF THE APPLICATION OF ATOMIC FORCE MICROSCOPY IN TESTING THE MECHANICAL PROPERTIES OF TWO-DIMENSIONAL MATERIALS

以石墨烯为代表,二维材料有着诸多优异的性质,在下一代电子器件等领域拥有广阔的应用前景.目前绝大多数关于二维材料的研究都集中在其电子学和光学的性质和应用,对于其力学性质的研究则相对欠缺,而力学性质在二维材料的研究和应用中都有着至关重要的意义.原子力显微镜是低维材料力学性质表征的主要手段,例如基于原子力显微镜的纳米压痕技术.本文首先简要介绍了二维材料的基本背景以及原子力显微镜的工作原理.进一步展示了纳米压痕技术的工作原理和理论背景,并回顾了利用纳米压痕技术研究二维材料面内力学性质的相关实验和理论工作,同时探讨了原子力显微镜在表征二维材料力学性能中存在的测量误差及来源.由于二维材料展现出强烈的各向异性,纳米压痕技术在能够很好地测量二维材料面内力学性质的同时,对于二维材料层间力学性质表征等方面存在明显的局限性.第三部分介绍了一种全新的基于原子力显微镜的埃(Å)压痕技术,该技术能够将形变尺度控制在0.1 nm以内,从而精确地表征和调控二维材料的层间范德华作用力,即层间力学性质.作者在第三部分介绍了通过埃压痕技术表征和调控的石墨烯、氧化石墨烯等二维材料的层间力学性质.最后简要介绍了范德华异质结材料的基本性质,探讨了埃压痕技术在该材料力学性质研究中的潜在应用.

Graphene and other two-dimensional(2D)materials possess various excellent properties and hold great promises for next generation of electronic devices and other applications.The mechanical properties are of fundamental importance in the research and application of 2D materials.Despite the fact that 2D materials have been extensively investigated in the past two decades,efforts on the mechanical properties are strikingly lacking and vastly needed.Atomic force microscopy(AFM)is one of the most widely used tools for the mechanical characterizations of low-dimensional materials.Particularly,the AFM-based nano-indentation technique has been extensively employed to explore the mechanical properties of 2D materials.In this review,we first introduce the basic backgrounds of 2D materials and atomic force microscopy.The mechanism and theoretical background of AFM-based nano-indentation are then demonstrated.In the second part,we review the research work by employing nano-indentation on studying the in-plane mechanical properties of 2D materials.The measurement errors of AFM-based nano-indentation and their origins are also discussed.Nanoindentation is perfectly suitable for the in-plane/intralayer mechanical measurement but also greatly limited in probing the out-of-plane/interlayer elasticity,due to the extreme anisotropy of 2D materials.Therefore,in the third part,we introduce an unconventional AFM-based technique-Angstrom-indentation which allows for sub-nm deformation on 2D materials.With such a shallow indentation depth comparable to the interlayer spacing of 2D materials,Angstrom-indentation is capable of measuring and tuning the interlayer van der Waals interactions in 2D materials.The interlayer elasticities of graphene and graphene oxide measured by Angstrom-indentation are discussed as examples in the third part.In the final part,we give a quick overview of a new type of 2D material-van der Waals heterostructure and its novel mechanical properties.We also discuss the potential application ofÅ-indentation in the investigation of the mechanical properties of van der Waals heterostructures.