Pattern Center Determination in EBSD
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In order to interpret the Kikuchi bands on a given EBSD pattern in terms of atomic geometry in the crystal, a reference frame for the image is required. The position of pattern center (PC) of EBSD is described by the point of intersection of a sphere of reflection with the plane of the photograph and indicates the relative position of the image with reference to the interaction volume of the sample. The techniques that can be used to locate PC on an EBSD are:
        (i) The conic fitting or three steel-ball method;
        (ii) The circular mask method;
        (iii) The known orientation method;
        (iv) Shadow casting; [1]
        (v) Iterative fitting; [2]
        (vi) Screen moving. [3]

These techniques offer accuracy ranging between 1% to 0.2% of the phosphor width for different PC components. Figure 2338a shows the pattern center for band identification in EBSD analysis.Here, the angle θ, prescribing the band width, follows the Bragg's law λ = 2dhklsin θ, and dhkl represents the d-spacing for reflecting plane. z* is the distance from the specimen to the screen.

The pattern center for band identification in EBSD analysis

Figure 2338a. The pattern center for band identification in EBSD analysis.

Figure 2338b shows the formation of a Ge (germanium) EBSD pattern projected onto a sphere centered at the PC. These kinematically simulated Kikuchi bands (the gray lines enclosing the bright bands) had been widened by a factor of 2 from their Bragg angles to ensure that the EBSD bands are fully enclosed.

formation of a Ge EBSD pattern projected onto a sphere centered at the PC (pattern center)

Figure 2338b. The formation of a Ge EBSD pattern projected onto a sphere centered at the PC. [4]

 

 

 

 

 

 

 

 

 

[1] Venables, J.A. & Bin Jaya, R. (1977). Accurate microcrystallography using electron back-scattering patterns. Phil Mag 35(5), 1317–1332.
[2] Krieger Lassen, N.C. (1999). Source point calibration from an arbitrary electron backscattering pattern.J Microsc 195, 204–211.
[3] Carpenter, D.A., Pugh, J.L., Richardson, G.D. & Mooney, L.R. (2007). Determination of pattern centre in EBSD using the moving-screen technique. J Microsc 227 (September), 246–247.
[4] Jay Basinger, David Fullwood, Josh Kacher, and Brent Adams, Pattern Center Determination in Electron Backscatter Diffraction Microscopy, Microsc. Microanal. 17, 330–340, 2011.

 

 

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