High-angle annular dark field imaging HAADF

Fig. 10. a Bright-field (BF) images of mesoporous silica with Pd Ru particles, b HAADF (high-angle annular dark field) images of mesoporous sihca with Pd Ru particles. c,d Electron-stimulated X-ray emission images prove that particles are intact. Reprinted with permission from [74]. Copyright (2001) American Chemical Society... 

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...

Fig. 6 — STEM imaging (200 kV Osiris STEM) combined with energy dispersive x-ray spectroscopy (EDX) of Pt-Pd catalytic nanoparticles. Unlike the high angle annular dark field (HAADF) image, EDX elemental mapping reveals the core shell structure of the nanoparticles. The high efficiency EDX system and high brightness electron source allows quickly obtaining elemental maps and statistically significant data within a realistic time frame. Total acquisition time was less than 12 minutes for (a) and less than 10 minutes for (b). The author would like to thank Dominique Delille (FEI company).

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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