有限厚度模型校准二维MoS2的Bimodal-AFM杨氏模量测量

二维材料因其独特的晶体结构、新奇的物理特性和优异的力学性能, 在微纳机电系统、柔性电子器件等诸多领域有着广阔的应用前景. 弹性模量是二维材料的基本力学特性参量之一, 对其器件应用及应变调控有重要影响. 受限于二维结构和原子级厚度特征, 难以实现二维材料弹性模量的精确测量. 双模原子力显微镜的振幅调制-频率调制模式是一种高效测量二维材料杨氏模量的方法, 但刚性衬底对测量结果的影响不可忽视. 本工作通过双模原子力显微镜直接测得衬底与二维硫化钼的杨氏模量分布图, 并基于有限厚度模型对衬底效应进行修正, 得到了样品的本征杨氏模量值. 利用第一性原理计算得到了二维二硫化钼的弹性系数和杨氏模量, 对比发现实验和计算结果相当. 这说明双模原子力显微镜测量是一种可靠的二维材料杨氏模量直接测试方法, 且该方法无需制备悬空二维材料等繁琐步骤, 避免了常规测试中的不足. 本工作为大面积二维材料薄膜力学性能的程序化测试分析以及高通量力学实验数据的统计分析提供了可靠的实验基础. 

THE FINITE THICKNESS MODEL CALIBRATES THE BIM ODAL-AFM YOUNG'S MODULUS MEASUREMENTS OF THE TWO-DIMENSIONAL MoS2

Because the two-dimensional (2D) materials possesses unique crystal structures, novel physical properties and excellent mechanical properties, the 2D materials is of broad application prospects in many fields including micro- and nano-electromechanical systems and flexible electronic devices, etc. The elastic modulus is one of the basic mechanical parameters for 2D materials, which is of an important influence on its device application and strain regulation. However, restricted by the characteristics of two-dimensional structure and atomic thickness, it is difficult to measure the accurate elasticity modulus of 2D materials. Amplitude modulation and frequency modulation within the bimodal atomic force microscopy is an efficient method for measuring Young's modulus of 2D materials, but the influence of rigid substrates cannot be ignored for the measurement results. In this work, the Young's modulus distribution of the substrate and 2D molybdenum sulfide were directly measured by the bimodal atomic force microscopy. Based on the finite thickness model, the intrinsic Young's modulus value of the sample was obtained after corrected the substrate effect. The elastic coefficient and Young's modulus of 2D molybdenum disulfide were calculated by the first principles calculation. The experimental results are consisted with the calculation results. That’s to say, the bimodal atomic force microscopy is a reliable direct characterization method for Young's modulus of 2D materials. This method does not require tedious steps like preparing suspended 2D materials, and can avoid shortcomings of conventional characterization methods. For thin films of large area two-dimensional materials, this work provides a reliable experimental basis for the programmed characterization analysis of their mechanical properties. Meanwhile, it provides firm experimental basis for future mechanistic statistical analysis of high throughput experimental data.