基于纳米压痕法的多孔硅硬度及杨氏模量与微观结构关系研究

Nanoindentation investigation of the hardness and Young's modulus of porous silicon depending on microstructure

采用电化学腐蚀制备多孔硅,利用场致发射扫描式电子显微镜(field emission scanning electron microscope,FESEM)观测多孔硅的二维微观形貌,利用Nano Indenter XP中的纳米轮廓扫描仪组件(nano profilometry,NP)得到其三维拓扑分析图像,分析了微观结构差异的原因并讨论了多孔硅内部微观结构对其机械性能的影响;利用MTSNano Indenter XP纳米压入测量仪器,研究了多孔硅的显微硬度和杨氏模量随压入深度的变化规律,比较了不同孔隙率多孔硅的机械性能差别.实验结果测得40mA/cm2,60mA/cm2,80mA/cm2和100mA/cm2四个不同腐蚀电流密度条件下制备多孔硅样品的孔隙率在60%-80%范围内,孔隙率随着腐蚀电流密度的增加而增大;在氢氟酸(HF)浓度为20%的条件下制备出多孔硅样品的厚度在40μm-50μm范围内;测得多孔硅的平均硬度、平均杨氏模量分别在0.478GPa-1.171GPa和10.912GPa-17.15GPa范围内,并且其数值随腐蚀电流密度的增加而减小,在纳米硬度范围内随压入深度的增加而减小,在显微硬度范围内其数值保持相对恒定,分析了样品表面、厚度、微观结构,及环境对其机械性能的影响,得到了多孔硅力学性能随其微观尺度形貌的变化规律.

In this paper, porous silicon （PS） was prepared by electrochemical etching method, its two-dimensional microstructure was observed by field emission scanning electron microscope （FESEM） and the three-dimensional topological image of PS was captured by Nano-Profilometry （NP）, thus the reason for the difference of PS microstructures was discussed and the effect of microstructure on its mechanical property was investigated. Using MTS Nano Indenter XP, the relationship between hardness and Young＇s modulus and the indentation displacement was studied and the mechanical property of PS with various porosities was compared. The experimental result showed that the porosity of PS prepared under various etching current densities （40,60,80 and 100 mA/cm^2） ranges from 60%--80%, which is increasing with the rising etching current density. The thickness of PS prepared under 20% HF is approximately 40--50 μm; the average value of hardness and Young＇s modulus of PS ranges from 0.478 GPa--1. 171 GPa and 10.912 GPa--17.15 GPa, respectively; and the values decrease with the etching current density rising, and decrease or keep constant with the displacement increasing in the range of nano-hardness and micro-hardness, respectively. The impact on PS mechanical property of its surface condition, thickness, microstructure and environment was analyzed and the relationship between PS mechanical property and microstructure was obtained.