Observing dislocations with ADF-STEM

Scanning transmission electron microscopy (STEM) with a high angle annular detector has become a useful technique in material science. The atomic number sensitive contrast (Z-contrast) of the Annular Dark-Field (ADF) image is good for looking at the distribution of heavy elements in a relatively light substrate. In many cases the impurity distributions are substantially affected by the defects in the materials and their interaction with the impurities. Therefore it is also desirable to observe defects with ADF images. This is possible and has some advantages over normal STEM. We have studied the ADF imaging of dislocations, its contrast mechanism and visibility in the ADF image.