module 3 - about the ebsd pattern
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
© Oxford Instruments Analytical Limited 2001
MODULE 3 - About the EBSD Pattern• Bragg Diffraction• Pattern Formation• ‘Background’• Background Subtraction• The Hough Transform• The information contained in the EBSP
© Oxford Instruments Analytical Limited 2001
About the EBSD Pattern - Bragg Diffraction
• EBSD occurs due to Bragg diffraction
• Bragg's law: nL = 2d sine thetawhere
• 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.
© Oxford Instruments Analytical Limited 2001
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.
© Oxford Instruments Analytical Limited 2001
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
© Oxford Instruments Analytical Limited 2001
About the EBSD Pattern - ‘Background’ Subtraction
• Background subtraction greatly enhances pattern contrast and the number of bands detectable
© Oxford Instruments Analytical Limited 2001
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
© Oxford Instruments Analytical Limited 2001
About the EBSD Pattern - Detecting the Bands - The Hough Transform
• Hough Transform of a single line
© Oxford Instruments Analytical Limited 2001
About the EBSD Pattern - Detecting the Bands - The Hough Transform
• Hough Transform of an EBSP
• Note the variation of gray scale in Hough Transform
© Oxford Instruments Analytical Limited 2001
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
© Oxford Instruments Analytical Limited 2001
About the EBSD Pattern - Information contained in the EBSP
The EBSP contains • the angular
relationship between planes
• the symmetry of the crystal
• orientation information
© Oxford Instruments Analytical Limited 2001
Examples
Pyrrhotite (6kV) Ferrite Aluminium
Titanium Olivine Ge