High-angle annular dark-field detector

S. J. Pennycook. EMSA Bulletin. 19, 67, 1989. A summary of compositional imaging using a high-angle annular dark-field detector in a field emission STEM instrument published by the Electron Microscopy Society of America, Box EMSA Woods Hole, MA 02543. 

S5mthetic resin-embedded alfalfa samples were oven dried at 65 °C for 24 h and cut at 40-90 nm. The slides were analyzed using a JEOL 2010-F TEM prepared with field emission gun, EDS, and a high angle annular dark field detector for the analysis of solitary nanoparticles. 

Fig. 7.6 Scheme of a scanning transmission electron microscope with bright- and dark-field detectors. ADF annular dark field HAADF high-angle annular dark field. (Adapted from [7]). 

Alternatively, images can be formed with electrons scattered at high angles (HAADF mode, for High Angle Annular Dark Field mode). An annular detector is placed below the sample and the focused electron beam is scanned over the sample. Interestingly, the contrast is not altered by diffraction phenomena and depends both the thickness and the composition (25). 

Fig. 3.14 Schematic set-up of an electron microscope in the transmission (TEM) (a) and combined (TEM and STEM) (b) modes. Note how the dark field detector is off the central axis, as the dark field image is based on scattered electrons. The HAADF-STEM operation mode with bright— (on the central axis) and dark-field detectors (of the central axis) is shown in (c). Two different modes are available for dark field imaging, i.e. annular dark field (ADF) high-angle annular dark field (HAADF). Figures modified after [37]. J. W Niemantsverdriet Spectroscopy in Catalysis An Introduction, pages 182 and 187. 2007. Copyright Wiley-VCH Verlag GmbH Co. KGoA. Reproduced with permission...

Observation by TEM (STEM) of the wear particles collected on the pin after a friction test performed with an IF-WS2/IF-M0S2 mixture shows the presence of sheets. By using a high-angle annular dark field (H A ADF) detector an image with a contrast depending on the atomic... 

Figure 2.52 TEM images of the IF-WS2/IF-M0S2 mixture obtained with a high-angle annular dark field (HAADF) detector. These images have a z-contrast that allows IF-WS2 and IF-M0S2 to be distinguished easily (Mo Z = 42 and W Z = 74)...

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