Optimal Conditions for Defect Analysis Using Electron Channeling Contrast Imaging

Abstract

The crystal defect analyses have been commonly conducted using transmission electron microscopy (TEM). There is no doubt that TEM is one of the best analyzing tool for examining crystal defects but limitations are bound to follow due to the shape of specimen; the thin foil (Williams & Carter, 2009). Recently, scanning electron microscopy (SEM) based technique for defect analysis, which is called electron channeling contrast imaging (ECCI), has got popularity. As a non-destructive and diffraction-based method, ECCI could take some advantages over analysis using TEM (Carnevale et al., 2015). In the first, the specimen preparation is relatively simple and only requires one side of a flat surface. It could exclude the concerns about whether defects to analyze are caused by the process of the specimen preparation or not. In addition, inspecting large area of flat surface could ensure the representativeness of the specimen. It is important to meet the exact Bragg-diffraction condition in order to distinguish dislocation lines from the background matrix (Simkin & Crimp, 1999). In the SEM, there are two approaches to achieve this condition. One is selected area channeling pattern (SACP), and the other is electron backscatter diffraction (EBSD). SACP could provide the rocking beam to induce electron channeling patterns (ECPs) in a small grain. With tilting the specimen, ECPs of the specific hkl-plane could move to meet the optic axis, i.e., the exact Bragg-diffraction condition. Despite its great angular accuracy, SACP has the poor resolution (Lloyd, 1987). Therefore it is almost impossible to conduct SACP at a few or sub-micrometer sized grain. The latter, EBSD, could overcome this situation. But it has its own limitation; poor angular accuracy. So we have to use both techniques to determine the Bragg-condition complementarily.