High-angle annular dark-field imaging

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... 

Figure 9 Nanostructured multicompartment cylinders, (a and b) Bright-field TEM images. Dark regions represent polypentafluorostyrene-chain-rich areas, (c and d) High-angle annular dark-field images of cylindrical micelles with internal phase-separated cores, (e) Cryogenic TEM image of uniform cylindrical micelles at 40% water/THF solution, (f) Cryogenic TEM image of cylindrical micelles with internal phase-separated cores at 67% water/THE solution. Chemical structures and schematic illustration of the formation of multicompartment cylinders (bottom). Reproduced with permission from...

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. 

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). 

Figure 3.134 TEM images of (a) 3-14 nm and (b) 8-14 nm Au-Fe304 nanodumbbells (c) High-angle annular dark-field scanning electron micrograph of the 8-9 nm Au-Fe304 particles ...

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