基于FIB和TEM的纳米材料中界面分层破坏的实验方法研究与应用

本文针对三维尺寸均处于纳米量级的材料与结构中常见的界面分层破坏问题,利用聚焦离子束技术(FIB)和透射电子显微镜(TEM)开发设计了一套研究纳米材料中界面端部裂纹启裂行为的实验方法.采用FIB成功从宏观多层薄膜材料(硅/铜/氮化硅,Si/Cu/SiN)中切割制备出了由硅基体(Si)和200 nm厚铜薄膜(Cu)及1000 nm厚氮化硅层(SiN)构成的纳米悬臂梁试样.利用高精度微小材料加载装置,在TEM中对该试样进行加载实验,并原位观测了不同试样中Cu/Si界面端部裂纹启裂的行为.通过对启裂瞬时Cu/Si界面上临界应力分布的有限元分析发现,不同尺寸试样中的界面上法向应力与剪切应力均集中在距界面端部100 nm的范围内,且临界法向应力远大于剪切应力.对应力分布的进一步分析则发现,距界面端部5 nm区域内的法向应力场控制着Cu/Si界面的分层破坏过程,可用于表征界面分层破坏的局部控制准则.

A FIB and TEM based experimental method for interface delamination in nanoscale materials and its application

To investigate the interface delamination in three-dimensional components in the nano-size, an experimental method is developed for the crack initiation at interface edge in nano-materials by using the focused ion beam（FIB） and the transmission electron microscopy（TEM）. With FIB, a nano-cantilever specimen consisting of 200-nm-thick copper（Cu） layer and 1000-nm-thick silicon nitride（SiN） layer on a silicon（Si） substrate is fabricated from a macroscale multi-layered material（Si/Cu/SiN） with the proposed method. By using a minute loading apparatus, the loading experiment is conducted in TEM, and the crack initiation at the edge of Cu/Si interface in different specimens is in situ observed. The detailed stress fields at crack initiation are analyzed with the finite element method, and both normal and shear stresses concentrate at the region of 100 nm from the interface edge in all specimens. In addition, the normal stress is much larger than the shear one. A close observation on stress fields shows that the normal stress field at the area 5 nm away from interface edge produces the local criterion for crack initiation at the edge of Cu/Si interface in nanoscale components.