Advancing Electron Backscatter Diffraction Characterisation Techniques with a Refined Approach to Indexing via Template Matching

Lead Research Organisation: Imperial College London
Department Name: Materials

Abstract

General overview

Electron backscatter diffraction (EBSD) is a characterisation technique used in the scanning electron microscope (SEM). EBSD allows the orientations and phases of the unit cell in a crystalline structure to be determined. Usually the patterns are indexed using a Hough transform, which can identify bands in the EBSP. The Hough, however, has shortcomings in that it doesn't take into account the finer features of the EBSP. The pattern matching approach has been introduced as a way to index EBSPs to account for the finer aspects of the pattern.

Objectives

To implement a faster and more accurate pattern matching approach to indexing EBSPs and demonstrate applications thereof.

Approach

- Update the current image cross correlation to use a fast Fourier transfer
- Demonstrate the updated indexing is accurate and precise enough to index real patterns
- Explore phase discrimination using multi-phase materials
- Demonstrate novel detector set ups using multiple detectors
- Use the new set up and indexing to determine the pattern centre of an EBSP

Novel content

- The updated Image correlation using a fast Fourier transform applied to an EBSP
- The refinement step to correct the first pass indexing
- Applying this to phase discrimination
- Using two direct electron detectors to collect and index two patterns simultaneously

Current progress

1 paper on preprint in ArXiv, currently under review in ultramicroscopy entitled "
Indexing Electron Backscatter Diffraction Patterns with a Refined Template Matching Approach." This paper demonstrates the new method of indexing and the refinement.
Preliminary data for proof of concept collected and analysed for phase discrimination using Zirconium hydride.
Sample of meteorite to use in phase discrimination polished and ready to EBSD.
Direct electron detectors tested and currently buying vacuum compatible components to use them.
Stage to hold the sample and detectors currently under construction.

Publications

10 25 50

Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509486/1 01/10/2016 30/09/2021
1857810 Studentship EP/N509486/1 01/10/2016 30/09/2020 Alexander Foden
 
Description New code for the indexing of electron backscatter patterns using a library of patterns has been generated. This uses a fast Fourier transform (FFT) to determine a close match to the pattern to be indexed and the associated shift to then perform a refinement in the orientation. The shift from the FFT allows for refinement in the x and y axes. To account for the z refinement, we exploit a log polar transform. This lets the rotation of the pattern to be read by an y shift between the pattern to be indexed and the best match from the library of images. currently the paper is under review
Exploitation Route Applying the method to phase identification in materials, such as zirconium hydride, where electron back scatter patterns are similar and the current method of distinguishing phases is inadequate.
Sectors Digital/Communication/Information Technologies (including Software),Manufacturing, including Industrial Biotechology

URL https://arxiv.org/abs/1807.11313