STEM image formation:

A Bright Field (BF) detector is placed in a conjugate plane to the back focal plane to intercept the direct beam while a concentric Annular Dark Field (ADF) detector intercepts the diffracted electrons.

The signals from either detector are amplified and modulate the STEM CRT. The specimen (Au islands on a C film) gives complementary ADF and BF images as can be seen by clicking the button opposite.

How does the ADF image described here differ from the dark field image described on the previous page?