Kikuchi diffraction pattern

Atlas of Backscattering Kikuchi Diffraction Patterns D J Dingley, K Z Baba-Kishi and V Randle ISBN 0 7503 0212 7... 

Since its development in the 1970s and 1980s, the electron backscatter diffraction (EBSD) technique has become the most widely used method for micro-texture investigations in recent years [150,151]. The EBSD system is usually attached to a Scanning Electron Microscope. By arranging the specimen at an appropriate angle, an electron diffraction pattern can be generated and captured on film, a camera or a screen. The diffraction pattern is called a Kikuchi diffraction pattern, which consists of pairs of parallel lines, each of... 

The Whole-Pattern symmetry is the symmetry which takes into account all the features present on a high S5mimetry zone axis diffraction pattern (i.e. the disks, the lines inside the disk and the Kikuchi lines). As mentioned above, in order to identify a 3D S5mimetry, the pattern should, at least, display the First-Order Laue Zone. In the example given on figure 2a, this FOLZ is weak, but clearly visible and the Whole Pattern displays a 3D-4mm S5munetry. 

Electron backscatter diffraction (EBSD) — The focused electron beam of Scanning Electron Microscopes (SEM) can be used to detect the crystallographic orientation of the top layers of a sample. The backscattered electrons (information depth 40-70 nm at 25 kV accelerating potential, lateral resolution around 200 nm) provide characteristic diffraction patterns (Kikuchi lines) on a phosphor screen. The patterns are recorded by a CCD-camera and interpreted by software. The position of the unit cell of the sample is determined by the corresponding Euler angles. In scanning mode, the software produces a surface orientation mapping that consists of... 

Other names instead of EBSD are Backscatter Kikuchi Diffraction (BKD), Electron Backscatter Pattern Technique (EBSP), Orientation Imaging Microscopy (OIM ), or Automated Crystal Orientation Mapping (ACOM). In combination with electrochemical studies only ex situ applications are possible. 

Figure 3 Examples of (a) selected area electron diffraction, (b) zone-axis CBED pattern, and (c) off-zone axis CBED pattern showing Kikuchi lines in the diffraction pattern...

Figure 3.14. Kikuchi lines in an electron diffraction pattern of quartz. g2 = 2420 is close to the exact Bragg angle. Compare with Figure 3.16(e, f).

Figure 3.16. Ewald sphere diagrams and the corresponding diffraction patterns showing the positions of the Kikuchi lines relative to the main Bragg beam, (a, b) jg = 0 (c, d) Sg < 0 and (e, f) = 0.

It is instructive to estimate the smallest tilt angle A0 which can be measured from displacements of Kikuchi lines. If we assume that a displacement of Ax = O.lx can just be measured, then from Eq. (3.59), A0 = (0.1)20, which is equal to about 0.05 degree with d = 0.5 nm and X = 0.004 nm. Thus, the accuracy with which an orientation can be determined from a diffraction pattern is greatly increased if Kikuchi lines are present. 

Reflexes and kikuchi-lines that appear on the electron diffraction patterns point out to the high degree of crystallization of the volume of these particles. 

CONTEXT X-ray diffraction is the most common method for determining molecular structures within a crystal, but other methods are capable of faster, less detailed information about the crystal. For example, electron backscatter diffraction (also called backscatter Kikuchi diffraction), from a scanning electron microscope, measures the diffraction patterns of electrons that scatter off more than one plane in the crystal. From the patterns, the crystallographic point group, the orientation of the crystal, and the exposed Miller indices of the surface can be determined. Copper crystals, which have the advantage of simple structure, have been used to test the strengths and limitations of this method. 

Using a Kikuchi pattern, one can tilt TEM specimen to a two-beam condition to get diffraction contrast imaging, or a zone axis to obtain diffraction patterns and HREM images. Figure 5.3 shows a schematic diagram of a Kikuchi map for... 

When the electrons impinge on the crystalline sample, they interact with individual lattice planes. When these interactions satisfy the Bragg condition, they exhibit backscattering diffraction and (due to the tilted sample) are directed toward a phosphor screen where the fluorescent pattern is detected by a CCD camera. The resulting pattern consists of a large number of intersecting bands, known as Kikuchi lines, which represent the unique crystallographic properties of the crystal... 

The corresponding SAD pattern of spots and Kikuchi lines is shown in Figure 3.16(b). The spacing between adjacent spots of the systematic row is X, and the Kikuchi lines Dj and Ex pass through the diffraction spots O and g, respectively. The second-order Kikuchi lines and Ei pass midway between —g and O and between g and Ig, respectively, and hence are a distance lx apart. 

The nature and origin of Kikuchi lines that arise from planes of the ZOLZ were discussed in Section 3.9. Kikuchi lines can also arise from HOLZ planes and are observed outside the diffraction disks of a CBED pattern. However, within the disks there are the so-called HOLZ lines, which are continuous with the HOLZ Kikuchi lines. 

Fig- 5 Kikuchi lines. The process is visualized as a labyrinthine game. The electron is the ball, bouncing in a variety of ways and emerging unpredictably after it has undergone diffraction. The spots form a pattern without any particular order, similar to the kikuchi lines. The student claimed not to have understood what the kikuchi lines are... 

When the surfaces of the samples are crystalline, electron backscatter diffraction (EBSD) patterns, called Kikuchi lines, generated from reflected electrons, are observed. EBSD patterns provide knowledge concerning crystal stmctures and orientations. Thus, the combination of SEM and EBSD is one of the powerful tools, which can tell us the microstmctures of the sample surfaces and the orientations of the grains on the sample surfaces. 

Several different types of diffraction condition are used to characterise radiation damage. These are achieved by tilting the specimen with reference to the Kikuchi pattern. These include dynamical two-beam , bright-field kinematical and weak-beam conditions - see Jenkins and Kirk for a full description. Under dynamical two-beam conditions, small dislocation loops located close to foil surfaces exhibit black-white contrast (Fig. 9.3), and their symmetry can be used to determine the Burgers vectors and habit-planes. 

Figure 11.11 Examples of RHEED patterns obtained during non-equilibrium MBE growth of GeSn alloys, (a) Pattern for a very smooth surface as in left side of Figure 11.10 showing points on an arc. The diagonal streaks are multiple diffraction effects known as Kikuchi bands.

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