Atomic-resolution defect contrast in low angle annular dark-field STEM

While traditional high-resolution STEM is performed by exclusively collecting electrons which have been scattered to high angles (i.e., HAADF), the present contribution will focus on small-angle scattered electrons, as in low angle annular dark-field (LAADF) STEM. This unique imaging mode allows one to image defect contrast while maintaining directly interpretable atomic resolution. By simply adjusting the microscope camera length, and thus the acceptance angle of the annular detector, it is possible to transition between Z-contrast and defect contrast. Both LAADF and HAADF experimental and computational results are discussed in regards to zone axis imaging of a γ / γ ′ Ni-superalloy; various length scales are explored. Electron de-channeling is observed while the probe is placed over defected regions of crystal.