Nano-beam electron diffraction

Transmission electron microscopy has been widely used for structural characterization of the irradiated microstmctures and is one of the primary techniques used for characterization of nano-sized defects in structural materials. These microscopes have been used for decades to characterize dislocations (size, density, type), voids, bubbles, and precipitates in materials, as well as grain sizes on the nanoscale and misorientalion of grain boundaries. In addition to imaging, semiquantitalive chemical compositions can be obtained using characteristic X-rays due to electron beam excitation. Electron diffraction provides structural information such as phases and ordering of the structure (amorphous versus crystalline). Improvements over the decades in... 

Fig. 7.17 Electron (nano) diffraction pattern from the double-chain structure of 2-line fer-rihydrite with the beam considered to be paralell to [001] (a-d), [010] (e) and [100] (f) respectively (Janney et al. 2000 with permission).

For FEG transmission electron microscopes, it is possible to demagnify the electron beam to a subnanometer electron probe. The diameter of the electron probe determines the sample area contributing to the (nano-) diffraction pattern. Electron nanodiffraction (END) makes possible the recording of a diffraction pattern from areas smaller than Inm. Therefore, END is the appropriate technique to study the structure of nanoparticles, as for instance nanotubes and quantum dots. Although a nanoprobe is a convergent beam, the convergence angle is usually smaller than in CBED. As will be shown, END is fundamental for STEM. 

---