=================================================================================
ADF-STEM (annular dark-field scanning transmission electron microscopy) as the main type of DF(dark-field)-STEMs is a powerful and common technique in modern EMs (electron microscopy) for acquiring high resolution images of materials, as presented by the pioneering works of Crewe and coworkers [1,2].
ADF-STEM is performed by collecting the electrons that have been scattered away from their incident direction. Figure 2799a shows the positions of the detectors which can be installed in a STEM system. Depending on the scattering angle of the transmitted electrons, various signals can be detected as a function of the position of the scanning probe: BF (bright-field)-STEM, DF (dark-field)-STEM or HAADF (high angle annular dark field)-STEM. The DF detectors are annularly shaped to maximize the collection efficiency and the range of the collected scattering angles can be adjusted through the magnification of the intermediate lenses.
![The positions of detectors in STEMs](image1/4538.jpg)
Figure 2799a. The positions of detectors in STEMs.
Figure 2799b illustrates the comparison of the main contrasts in both CTEM and STEM modes.
![Comparison of the main contrasts in both CTEM and STEM modes](image1/4113aa.gif)
Figure 2799b. Comparison of the main contrasts in both CTEM and STEM modes.
[1] J. Wall, J. Langmore, M. Isaacson, A.V. Crewe, Proc. Natl. Acad. Sci. USA 71
(1974) 1.
[2] A.V. Crewe, J.P. Langmore, M.S. Isaacson, in: B.M. Siegel, D.R. Beaman (Eds.),
Physical Aspects of Electron Microscopy and Microbeam Analysis, Wiley and
Sons, New York, 1975, pp. 47–62.
|