Mechanical department seminar "Non-destructive characterization of crystalline defects in bulk samples".

Electron microscopy is a widely used technique for analyzing the micro- and nanostructures of crystalline materials. Two main types of electron microscopes provide complementary information: transmission electron microscopy (TEM) at the micro/nano scale and scanning electron microscopy (SEM) at the macro/mesoscopic scale.

TEM is well established for characterizing crystalline defects at submicron and nanoscale levels in electron-transparent thin films (around 100 nm thick). These detailed studies provide crucial information for understanding the macroscopic behavior of the material.

However, the characterization of crystalline defects is not limited to thin sheet samples observed by TEM. SEM can also provide diffraction contrast in bulk materials thanks to electron channeling. This phenomenon occurs when electrons move along crystal planes, allowing deeper penetration before scattering. Variable backscattering of electrons from different crystal orientations generates orientation contrast, enabling imaging of crystal defects.

Electron Channeling Contrast Imaging (ECCI) is a non-destructive technique that enables imaging of sub-surface defects (down to around 100 nm in depth) on centimeter-sized bulk samples inside an SEM. The technique exploits the significant variation in backscattered electron yield (BSE) as a function of crystal orientation with respect to the incident electron beam or the optical axis of the SEM.

Thanks to these capabilities, ECCI has become a powerful tool for exploring new frontiers in fundamental and industrial research. This presentation will provide an overview of the technique, covering its underlying physics and its various applications in these fields.