Annular dark-field imaging

Annular dark-field imaging is a method of mapping samples in a scanning transmission electron microscope (STEM).

[1] Conventional TEM dark-field imaging uses an objective aperture to only collect scattered electrons that pass through.

This gives an advantage in terms of signal collection efficiency and allows the main beam to pass to an electron energy loss spectroscopy (EELS) detector, allowing both types of measurement to be performed simultaneously.

Because of this, the HAADF detector senses a greater signal from atoms with a higher Z, causing them to appear brighter in the resulting image.

With this in mind, a common application for HAADF is in heterogeneous catalysis research, as determination of the size of metal particles and their distribution is extremely important.