High-angle annular-dark field

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. 12. Schematic of the information from HRSTEM, DF, and high-angle annular dark-field (HAADF) microscopy.

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]). 

HAADF high-angle annular dark field... 

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). 

A recent flurry of activity in aberration correetion has been partially prompted by the ease of reliable precision lens control offered by the personal computer and the computer-aided tuning of complex lens systems. Several demonstration models have been developed for TEM [3.44], SEM [3.45] and STEM [3.46] that illustrate the general validity of the eoneept. The application of spherical aberration correctors is most effective in dedieated STEM because it suffers less from chromatic aberration due to a lack of post-specimen lenses (for example for high-angle annular dark-field imaging). 

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... 

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