New techniques for imaging and identifying defects in electron microscopy

Abstract

Defects in crystalline materials control the properties of engineered and natural materials, and their characterization focuses our strategies to optimize performance. Electron microscopy has served as the backbone of our understanding of defect structure and their interactions owing to beneficial spatial resolution and contrast mechanisms that enable direct imaging of defects. These defects reside in complex microstructures and chemical environments, demanding a combination of experimental approaches for full defect characterization. In this article, we describe recent progress and trends in methods for examining defects using scanning electron microscopy platforms, where several emerging approaches offer attractive benefits, for instance in correlative microscopy across length scales and in situ studies of defect dynamics.

Microstructure, Deformation, and Property of Wrought Magnesium Alloys

“…To reveal the origin of the texture change, the EBSD technique needs to be combined with other techniques that are capable of providing texture and chemical information at a much finer scale. The emerging techniques of transmission Kikuchi diffraction (TKD) [298] and transmission scanning electron microscopy (TSEM) [299] have a spatial resolution of tens of nanometres, which are an order of magnitude better than EBSD. The combined use of these diffraction and imaging techniques, together with energy-dispersive X-ray spectroscopy (EDXS) mapping technique, offers an opportunity for collecting texture and chemistry information from a nano-sized recrystallized grain and its neighboring deformed grain(s).…”

Advances in in situ nanomechanical testing

“…Due to the multiscale and complex nature of defect structures in deformed materials, correlative microscopy techniques in scanning electron microscopy can provide unique insights. In their article in this issue, Gianola et al 16 discuss some of the emerging SEM-based methods for identifying defects, including EBSD, ECCI, and diffraction-contrast STEM. EBSD continues to evolve with faster detectors that enable in situ mechanical testing combined with ECCI and diffraction-contrast STEM, and higher resolution imaging that allow for defect characterization.…”

Advancing characterisation with statistics from correlative electron diffraction and X-ray spectroscopy, in the scanning electron microscope

“…Loading colour map is unnormalised between maps to show contrast 2 . No PC strongly contributes to the highlighted grain (1)(2)(3)(4)(5)(6), and the VARIMAX rotated component that most loads it (f) includes significant signal from several other precipitates and matrix. This results in the corresponding RC-EBSP being dominated by FCC Co signal, and indexing accordingly (point C in Figure 7).…”

“…Progress towards rapid, accurate and statistically robust characterisation of microstructures has been made in recent years with developments in both experimental techniques and data processing. There has been interest in 'correlative' microscopy, where multiple techniques are employed to access independent information channels sampled from the same area of interest (AOI) [1][2][3]. Successful use of correlative microscopy yields superior characterisation capability (as limitations of individual techniques may be mitigated) and provides better confidence in phase assignment if independent classifications are mutually inclusive.…”