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MODULE 3 - About the EBSD Pattern

MODULE 3 - About the EBSD Pattern. Bragg Diffraction Pattern Formation ‘Background’ Background Subtraction The Hough Transform The information contained in the EBSP. About the EBSD Pattern - Bragg Diffraction. EBSD occurs due to Bragg diffraction Bragg's law: nL = 2d sine theta. where

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MODULE 3 - About the EBSD Pattern

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  1. MODULE 3 - About the EBSD Pattern • Bragg Diffraction • Pattern Formation • ‘Background’ • Background Subtraction • The Hough Transform • The information contained in the EBSP

  2. About the EBSD Pattern - Bragg Diffraction • EBSD occurs due to Bragg diffraction • Bragg's law: nL = 2d sine theta • where • n is the order of reflection, • L (Lambda) is the electron wavelength, • d is the lattice spacing, and • theta is the Bragg angle, the angle of incidence of the electron.

  3. About the EBSD Pattern - Pattern Formation • Electron scattering takes place between the crystal planes • Bragg diffraction occurs from the crystal planes • Bands in the EBSP are called Kikuchi bands.

  4. About the EBSD Pattern - ‘Background’ • Only a small proportion of the electrons arriving at the phosphor screen are diffracted. • Therefore the pattern is superimposed on a ‘background’ • Background subtraction is required to enhance pattern contrast

  5. About the EBSD Pattern - ‘Background’ Subtraction • Background subtraction greatly enhances pattern contrast and the number of bands detectable

  6. About the EBSD Pattern - Detecting the Bands - The Hough Transform • The Hough Transfrom provides a suitable technique for deriving the parameters of a straight line and thus the band positions in an EBSP. • Lines in the pattern are converted to ‘spots’ in Hough Space

  7. About the EBSD Pattern - Detecting the Bands - The Hough Transform • Hough Transform of a single line

  8. About the EBSD Pattern - Detecting the Bands - The Hough Transform • Hough Transform of an EBSP • Note the variation of gray scale in Hough Transform

  9. About the EBSD Pattern - Detecting the Bands - The Hough Transform • Filtering the Hough Space image greatly enhances clarity • Peak detection is used to find the maxima • Band positions are determined and related back into real space

  10. About the EBSD Pattern - Information contained in the EBSP The EBSP contains • the angular relationship between planes • the symmetry of the crystal • orientation information

  11. Examples Pyrrhotite (6kV) Ferrite Aluminium Titanium Olivine Ge

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