Optimizing disk registration algorithms for nanobeam electron diffraction strain mapping.
Scanning nanobeam electron diffraction strain mapping is a technique by which the positions of diffracted disks sampled at the nanoscale over a crystalline sample can be used to reconstruct a strain map over a large area. However, it is important that the disk positions are measured accurately, as their positions relative to a reference are directly used to calculate strain. In this study, we compare several correlation methods using both simulated and experimental data in order to directly probe susceptibility to measurement error due to non-uniform diffracted disk illumination structure. We found that prefiltering the diffraction patterns with a Sobel filter before performing cross correlation or performing a square-root magnitude weighted phase correlation returned the best results when inner disk structure was present. We have tested these methods both on simulated datasets, and experimental data from unstrained silicon as well as a twin grain boundary in 304 stainless steel.
Department of Materials Science and Engineering, University of California, Berkeley, Berkeley, USA 94720; National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, USA 94720.
Thomas C
TC
Pekin
Erich Schmid Institute of Materials Science, Jahnstrasse 12, Leoben, Austria 8700.
Christoph
C
Gammer
National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, USA 94720.
Jim
J
Ciston
Department of Materials Science and Engineering, University of California, Berkeley, Berkeley, USA 94720; National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, USA 94720.
Andrew M
AM
Minor
National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, USA 94720. Electronic address: cophus@gmail.com.
Colin
C
Ophus
Nanobeam electron diffraction; Strain measurement