Page 331 - Book Hosokawa Nanoparticle Technology Handbook

FUNDAMENTALS CH. 5 CHARACTERIZATION METHODS FOR NANOSTRUCTURE OF MATERIALS

Figure 5.5.6
The comparison of bright-field image and dark-field image of aluminum alloy.

Thin/low density Thick/high density

Objective lens

Objective aperture Back focal plane

Image plane
Intensity

Figure 5.5.7
Mass-thickness contrast.
Figure 5.5.8
in signals, detected through various STEM detectors, High-resolution TEM image of beta Si N seen from c-axis.
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allows one to build up a 2D image of the specimen.
Furthermore, using a high-angle annular dark-field
detector, Z-contrast imaging can be carried out. By 5.5.2 Analytical TEM (AEM)
using a Scanning TEM (STEM) detector with a large
inner radius, electrons are collected which are not 5.5.2.1 Energy dispersive X-ray spectroscopy (EDS)
Bragg scattered. As such Z-contrast images show lit- EDS is a method for qualitative and quantitative ele-
tle or no Bragg scattered events, their intensity is mental analysis using X-rays, which have unique
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approximately proportional to Z . Z-contrast imaging energies from each element. The characteristic X-ray
using a high-angle annular dark-field (HAADF) spectrum is caused by the de-energization of the atom
detector is particularly useful for investigating high-Z after an inelastically scattered electron is produced
materials within a low-Z material. A HAADF detector (Process 1 in Fig. 5.5.9). A lower-shell electron is
collects electrons that undergo high-angle scattering, emitted from the atom during process 1 and there is a
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and the signal is approximately proportional to Z . vacancy at the lower shell. A higher-shell electron can
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