氧化硅薄膜中界面脱层协同演化导致的弯曲裂纹形貌形成

Formation of wavy crack morphology in silicon oxide films due to collaborative interface debonding

当薄膜以适当的黏附能结合在基底上时,由于残余拉伸应力的作用,薄膜会同时发生开裂和界面脱层,从而形成许多不同寻常的裂纹形貌,如螺旋、新月以及各种取向的条状.在实验上采用溶胶凝胶法制备二氧化硅溶胶,溶胶镀在玻璃基片上后,通过高温干燥引入热应力,得到了大量迥异的裂纹形貌,如直线型裂纹网络、弯曲裂纹网络以及直线型裂纹与弯曲裂纹共存的裂纹网络.光学显微镜和扫描电子显微镜观测显示弯曲裂纹与直裂纹的共存与转变和薄膜裂纹扩展是否伴随界面脱层密切相关.对在不同薄膜厚度下得到的新月裂纹进行观测,发现一定范围内新月裂纹波长与厚度之间存在线性关系.本文也报道了一些其他的特殊裂纹形貌,以及几种弯曲裂纹的生长过程.最后提出了模拟界面脱层与开裂协同演化过程的相场方法,期待未来进一步揭示弯曲裂纹形貌形成的更多细节.

When a thin film moderately adherent to a substrate is subjected to residual tensile stress, the cooperation between film crack and interface debonding leads to unusual crack patterns, such as spirals, alleys of crescents and variously oriented strips. We use sol-gel method to fabricate silica sol, and then get a film-glass-substrate system via spin coating technique. Many unique crack morphologies are observed after high temperature drying, such as straight-sided crack network, wavy crack network and their coexistence. The optical microscope and scanning electron microscope reveal that the coexistence and transition of these two kinds of crack networks are closely related to whether the interface debonding occurs simultaneously or not. There is a linear relationship between wavelength and thickness of the crescent crack. Some other unique crack patterns and their growth processes are observed as well. Finally, we propose a phase field simulation tool to study the evolution of film cracking with the concurrent interface debonding. It is worthwhile to further elucidate how the interface debonding facilitates formation of the wavy crack network by using such phase field modeling in future.