M.C. Brandes

Diffraction contrast STEM of dislocations: imaging and simulations.

The application of scanning transmission electron microscopy (STEM) to crystalline defect analysis has been extended to dislocations. The present contribution highlights the use of STEM on two oppositely signed sets of near-screw dislocations in hcp α-Ti with 6wt% Al in solid solution. In addition to common systematic row diffraction conditions, other configurations such as zone axis and 3g imaging are explored, and appear to be very useful not only for defect analysis, but for general defect observation. It is demonstrated that conventional TEM rules for diffraction contrast such as g·b and g·R are applicable in STEM. Experimental and computational micrographs of dislocations imaged in the aforementioned modes are presented.

Zone Axis STEM Defect Imaging Based on Electron Kossel Patterns

orientation, i.e., with the beam direction, B , parallel to a principal zone. It was noted that the zone axis image quality, and hence defect contrast, are strongly dependent on the particular zone chosen. In this contribution, we propose that the defect image contrast quality from a given zone is directly related to the electron Kossel pattern (EKP), which is a function of crystal structure, orientation, and thickness, as well as the accelerating voltage.