Electron microscopy: probing the atomic structure and chemistry of grain boundaries, interfaces and defects

At the heart of ‘ dynamic embrittlement’ phenomena is the stress-induced segregation of microscopic quantities of embrittling impurities to fracture surfaces. Grain boundaries and interfaces are often the natural weak links in a material. The structural and chemical information of such internal interfaces can be probed on an atomic scale using transmission electron microscopy. High-resolution electron microscopy can be used to determine the atomic coordinates of crystalline interfaces. Electron-energy-loss spectroscopy (EELS) and energy-dispersive X-ray spectroscopy can be performed on any boundary or defect and can provide chemical information such as composition and bonding. The spatial resolution of EDS is limited by low collection efficiency to around 10 Å. The more efficient signal collection for EELS allows almost atomic resolution for light elements. EELS fine structure offers a fingerprint of the local boundary arrangements, and also insight into the bonding (and possible reactivity) of boundaries and other defects. Overall, electron microscopy can be used to identify the atomistic characteristics of those interfaces susceptible to dynamic embrittlement. The structural and electronic information obtained can be used as a starting point for semi-empirical and ab initio simulations.