Scanning electron microscopy imaging of dislocations in bulk materials, using electron channeling contrast

Abstract

The imaging and characterization of dislocations is commonly carried out by thin foil transmission electron microscopy (TEM) using diffraction contrast imaging. However, the thin foil approach is limited by difficult sample preparation, thin foil artifacts, relatively small viewable areas, and constraints on carrying out in situ studies. Electron channeling imaging of electron channeling contrast imaging (ECCI) offers an alternative approach for imaging crystalline defects, including dislocations. Because ECCI is carried out with field emission gun scanning electron microscope (FEG-SEM) using bulk specimens, many of the limitations of TEM thin foil analysis are overcome. This paper outlines the development of electron channeling patterns and channeling imaging to the current state of the art. The experimental parameters and set up necessary to carry out routine channeling imaging are reviewed. A number of examples that illustrate some of the advantages of ECCI over thin foil TEM are presented along with a discussion of some of the limitations on carrying out channeling contrast analysis of defect structures.

Dark-field imaging based on post-processed electron backscatter diffraction patterns of bulk crystalline materials in a scanning electron microscope

“…The magnification must be high enough (higher than  100) for the beam to specimen surface angle to be considered as constant over the whole scanned area. Then, if an ECP is recorded, a specific reflection can be selected by rotating and tilting the specimen in order to bring a particular pseudo-Kikuchi line or a zone axis at the center of the ECP image [11][12][13][14] to obtain a new image related to the new area brought at the center of the ECP. Unfortunately, this facility being only available by tilting and rotating the specimen in the SEM, this limits greatly the applicability of such a technique.…”

The defect evolution in shock loaded tantalum single crystals

“…On the dislocation images with brighter background (w > 0), the dislocation image is brighter on one side and darker on the other [62].…”

“…Crimp [62] carried out an in-situ experiment on a titanium alloy. In his study, dislocation densities were measured by counting the dislocations in the image [62]. A di↵erent method was also employed by Gutierrez-Urrutia on iron.…”

Polycrystalline Diamond (PCD) Tool Material: Emerging Applications, Problems, and Possible Solutions

“…In the author's opinion, the first and foremost stage in further PCD development should be concerned with the quantification of microcrack structure [31]. Special techniques to classify, count and measure the length, spacing and orientation of microcracks should be developed for PCDs and other tool materials using the available methodologies and test equipment (e.g., the electron channeling contrast methodology using CamScan 44 FE SEM equipped with a Schottky thermal field emission gun [32]). Digital image processing should be applied to take the measurements, thereby providing time effective, reproducible, statistically significant estimates of crack morphology.…”