Large angle CBED

The advantage of being able to record diffraction intensities over a range of incident beam directions makes CBED readily accessible for comparison with simulations. Thus, CBED is a quantitative diffraction technique. In past 15 years, CBED has evolved from a tool primarily for crystal symmetry determination to the most accurate technique for strain and structure factor measurement [16]. For defects, large angle CBED technique can characterize individual dislocations, stacking faults and interfaces. For applications to defect structures and structure without three-dimensional periodicity, parallel-beam illumination with a very small beam convergence is required. 

Figure 4 (a) Schematic illustration of large-angle CBED technique and (b) an example of LACBED pattern taken from Si near [113] zone axis showing high order Laue zone lines in the disk... 

Electron Diffraction (SAED), Microdiffraction, Convergent-Beam Eleetron Diffraetion (CBED), Large-Angle Convergent-Beam Eleetron Diffraetion (LACBED) and electron precession. They produee spot, ring, disk or line patterns at microseopie or nanoseopie seales in eorrelation with the image of the diffracted area. An overview of the main applieations is given. 

For a long time, Selected-Area Electron Diffraction (SAED) performed with a parallel incident beam and a selected-area aperture was the only experimental method available. During the three last decades, new diffraction techniques based on a convergent electron incident beam (CBED Convergent-Beam Electron Diffraction, LACBED Large-Angle... 

Electron Diffraction (CBED) and Large-Angle Convergent-Beam Electron Diffraction (LACBED) allow the identification of the crystal system, the Bravais lattice and the point and space groups. These crystallographic features are obtained at microscopic and nanoscopic scales from the observation of symmetry elements present on electron diffraction patterns. 

Convergent beam electron diffraction (CBED) strictly refers to diffraction using an electron probe in a TEM with very large convergence angle. When this convergence angle becomes small the conditions are similar to the spot pattern obtained with parallel illumination in the conventional Selected Area Diffraction Patterns (SADP) as is shown in Fig. 1. 

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