Kikuchi pattern

Figure 3.38 Kikuchi pattern of a silicon foil symmetrically oriented along the [111] zone. The pattern reveals six-fold symmetry. (Reproduced with permission from S. Amelinckx et al., Handbook of Microscopy Applications in Materials Science, Solid-State Physics and Chemistry, Wiley-VCH Verlag GmbH, Weinheim. 1997 Wiley-VCH.)...

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. 

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... 

Tilt the specimen to a zone axis. To get better HREM images, a thin area is preferred. At thin areas, it is difficult to see Kikuchi pattern even using CBED technique. Thin specimen tends to bend easily, so it is necessary to make sure the area you are going to image is right on zone axis using CBED pattern. 

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. 

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

Hatakeyama H, Kikuchi A, Yamato M et al (2007) Patterned biofunctional designs of ther-1172 moresponsive surfaces for spatiotemporally controlled cell adhesion, growth, and thermally 1173 induced detachment. Biomaterials 28(25) 3632-3643... 

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. 

A grating pattern from a single crystal containing misorientations of 5°. (d) As for Fig. 4(b), but given a very light etch. Kikuchi lines are visible indicating that material of high perfection has been exposed. 

Two isomers of Y Cg2 (I, II) have been separafed and isolafed by fhe fwo-sfage HPLC mefhod (Inakuma ef al., 1995 Kikuchi ef al., 1994b Shinohara ef al., 1995a,b). Bofh isomers of Y Cg2 show disfincf ESR h)q5erfine doublefs due fo f = 1/2 yttrium nucleus. The overall ESR specfral patterns of Y Cg2 (I, II) in CS2 solufion af room femperafure are similar, buf fhe hfs values differ. Moreover, fhe appearance of fhe small safellife peaks due to adjacent to the main doublets, is much less clear in Y Cg2 (II). Obviously, the electronic structures of fhe fwo isomers are differenf. If has been found fhaf isomer (II) is less sfable in air and much more reactive toward various solvents than isomer (I). Yamamoto et al. (1997) produced and isolated three isomers of La C9o (I-III) and observed the hfs. The observed hfc values are much smaller fhan those of... 

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...

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... 

K. Ariga, J. Kikuchi, M. Naito, E. Koyama, N. Yamada, Modulated Supramolecular Assemblies Composed of Tripeptide Derivatives Formation of Micrometer-Scale Rods, Nanometer-Size Needles, and Regular Patterns with Molecular-Level Flatness from the Same Compoimd , Langmuir, 16,4929 (2000)... 

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).

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. 

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. 

The volume of specimen contributing to a CBED pattern is much smaller than that contributing to an SAD pattern. Thus, there is less likelihood that the effects of strain, specimen bending, or crystal defects will influence the nature of a CBED pattern. Consequently, Kikuchi lines are usually more often observed and are usually clearer in CBED patterns than in SAD patterns. 

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. 

Cosse et al. showed that EF decreases as the thickness of anodized Al-0.5%Cu films increases from 3 to 10 J.m.32 Kikuchi et al. reported that EMM of Al specimens resulted in the hemispherical 20-pm-deep microgrooves.40 In this case, porous-type anodization of patterned Al substrates was isotropic. These results suggest that localized anodization becomes isotropic as the anodization process proceeds. These conclusions are consistent with those obtained with other EMM methods, which indicate that EF decreases as the depth of metal removal increases.13,17... 

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