HAADF detector

As shown above, the size and distribution of minute particles are conveniently investigated by high-resolution STEM with a HAADF detector (60,63). The intensity in HAADF images is a monotonic function of the sample thickness and atomic number, a pre-requisite for the electron tomography experiments described below. 

Fig. 9 Z -contrast imaging and EELS. The electron probe is scanned across the sample. For each scan position, the HAADF detector collects the high-angle scattering intensity. The intensity of one scan-position is represented as the corresponding pixel intensity in the STEM image. The forward scattered beam is not affected by the detector and can be used for EELS. (View this art in color at www.dekker. com.)...

As schematically shown in Fig. 5.13a, when incident electrons go through a cloud of electron of an atom, the incident electron is scattered due to attraction of nuclear. With a HAADF detector, only high angle Rutherford scattering is collected. The cross-section of Rutherford scattering depends on the square of atomic number Z. So, a HAADF image is a Z-contrast image. 

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)...

Figure 3.67 (a) TEM image obtained with an HAADF detector with corresponding chemical mapping of (b) Ni, (c) O, (d) Y and (e) Fe. These analyses show the presence of catalyst and iron oxide in these carpets... 

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