Transmission electron microscope observation of cracks introduced in bulk crystals

材料断裂是材料科学中最重要的学科之一。材料断裂的研究有两种方法。一种是宏观模拟，另一种是用计算机进行原子模拟。然而，这两个极端之间存在着巨大的差距，而正是介观尺度上的信息弥合了这一差距。为了在介观尺度上获得这样的信息，透射电子显微镜应该是最合适的技术。然而，含有S裂纹尖端的薄片试件的制备是极其困难的，本研究的目的是利用聚焦离子束技术从裂纹尖端等预选区域制备薄箔试件，并对大块晶体中引入的裂纹进行透射电子显微镜检查。这在很大程度上弥合了宏观方法和原子模拟之间的差距。本文以Si、GaAs、Al_2O_3和准晶为试件，对裂纹尖端及其附近的缺陷结构进行了全面的观察。

Fracture of materials is one of the most important subjects in materials science. There are two approaches to the study of fracture of materials. One is macroscopic one and the other is atomistic simulation using a computer. However, there is a big gap between these extremes and it is information on mesoscopic scale that bridges this gap. In order to get such information on mesoscopic scale transmission electron microscopy should be the most appropriate technique. However, it is extremely difficult to prepare a foil specimen which contain S the very tip of a crack.The purpose of the present study is to examine by transmission electron microscopy those cracks which were introduced in bulk crystals applying a focused ion beam technique to preparation of a thin foil specimen from pre-selected area such as a crack tip. This contributes much to bridge the gap between macroscopic approach and atomistic simulation. In this study, Si, GaAs, alumina and quasicrystals were used as specimens and the defect structures at and near the tips of the cracks were observed comprehensively.