纳米尺度界面分层破坏行为的实验研究与分析

Investigation on the cracking behavior of nanoscale interface delamination

为系统研究纳米尺度材料中的界面分层破坏行为,基于悬臂梁弯曲法,利用聚焦离子束技术,从宏观多层薄膜材料(硅/铜/氮化硅,Si/Cu/Si N)中制备出了不同类型的(直、扭转)纳米悬臂梁试样,用以开展相应的实验研究。之后,在透射电子显微镜中分别对直纳米悬臂梁和扭转纳米悬臂梁试样进行原位加载实验。在直纳米悬臂梁试样中,Cu/Si界面受到由弯矩导致的拉应力而发生分层破坏;在扭转纳米悬臂梁试样中,通过改变加载点的位置调整界面上正应力与剪应力的比值,开展了不同复合型的界面裂纹启裂实验。利用有限元法分析了临界载荷作用下Cu/Si界面上的应力场,发现所有试样的应力集中区域均在距界面端部100 nm的范围内。在直纳米悬臂梁试样中,法向应力控制着Cu/Si界面端部的裂纹启裂行为,为单一型分层破坏;在扭转纳米悬臂梁试样中,界面裂纹启裂时的临界正应力与剪应力之间存在着一个圆形准则。

Different types of nano-cantilever specimens are fabricated from a macroscale multilayered thin film(silicon/copper/silicon nitride, Si/Cu/Si N) by using the Focused Ion Beam(FIB) based on the cantilever bending method in order to investigate the cracking behavior of nanoscale interfaces. For the single-mode interface cracking, a straight nano-cantilever specimen is fabricated. For the mixed-mode interface cracking, a double-nano-cantilever specimen is proposed to simultaneously apply bending and torque moments to the interface. All specimens are in situ loaded in the Transmission Electron Microscopy(TEM). In straight nano-cantilever specimens, the Cu/Si interface fractures due to a bending moment. In torsion nanocantilever specimens, by changing the loading position, fracture experiments with different mode-mixities are successfully conducted. In addition, finite element analysis is employed to inquire the critical stress distribution on interface during the crack initiation, and stress concentration regions near the interface edge in all specimens are within the scale of 100 nm. In straight nano-cantilever specimens, the interfacial normal stress dominates the interface cracking, indicating a single-mode fracture. In torsion nanocantilever specimens, the critical normal and shear stresses at crack initiation have a circular relation.