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SUMMARY:Crystallography and strain mapping: some new theory for Geometric 
 Phase Analysis (GPA) - Prof. Martin Hytch\, CEMES-CNRS
DTSTART:20190408T090000Z
DTEND:20190408T100000Z
UID:TALK121450@talks.cam.ac.uk
CONTACT:Duncan Johnstone
DESCRIPTION:Over the years\, geometric phase analysis of HR(S)TEM images h
 as become a widely used technique for\nstrain mapping. Whilst successful\,
  the approach is not without limitations. An internal\nreference of undist
 urbed crystal must be present within the field of view and the regions of 
 crystal to\nbe analysed must have common\, or closely related\, reciprocal
  lattice vectors. Even in the presence of\nan internal reference\, elastic
  strains should be determined relative to the relaxed crystal structure\,\
 nwhich is not necessarily the same as the reference used for the analysis.
 \nHere\, we present a major extension of GPA that addresses these problems
 . It allows the study of strain\nin nanocrystals\, where no reference regi
 on is generally present\, in epitaxial heterostructures\, where\nthe mater
 ials can be very different from the substrate\, and across grain boundarie
 s\, where no common\nlattice planes in general exist. The new theory is ba
 sed on adding crystallographic information to the\nanalysis. In so doing\,
  the reference problem\, large lattice rotations and global optical distor
 tions can be\ndealt with. It is little known\, for example\, that a global
  shear applied to an image will cause errors to\nconventional strain analy
 sis. We apply the method to some representative examples and highlight the
 \nimplications for other strain mapping techniques based on images or diff
 raction.
LOCATION:Goldsmiths 1\, Lecture room\, Dept. of Materials Science and Meta
 llurgy
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