title: Artefacts in geometric phase analysis of compound materials.
abstract: The geometric phase analysis (GPA) algorithm is known as a robust and straightforward technique that can be used to measure lattice strains in high resolution transmission electron microscope (TEM) images. It is also attractive for analysis of aberration-corrected scanning TEM (ac-STEM) images that resolve every atom column, since it uses Fourier transforms and does not require real-space peak detection and assignment to appropriate sublattices. Here it is demonstrated that, in ac-STEM images of compound materials with compositionally distinct atom columns, an additional geometric phase is present in the Fourier transform. If the structure changes from one area to another in the image (e.g. across an interface), the change in this additional phase will appear as a strain in conventional GPA, even if there is no lattice strain. Strategies to avoid this pitfall are outlined.
authors.affiliation: Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, United Kingdom. Electronic address: j.j.p.peters@warwick.ac.uk.
authors.forename: Jonathan J P
authors.initials: JJ
authors.lastname: Peters
authors.affiliation: Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, United Kingdom.
authors.forename: Richard
authors.initials: R
authors.lastname: Beanland
authors.affiliation: Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, United Kingdom.
authors.forename: Marin
authors.initials: M
authors.lastname: Alexe
authors.affiliation: Department of Physics and Astronomy, University of Sheffield, Hounsfield Road, Sheffield S3 7RH, United Kingdom.
authors.forename: John W
authors.initials: JW
authors.lastname: Cockburn
authors.affiliation: Department of Physics and Astronomy, University of Sheffield, Hounsfield Road, Sheffield S3 7RH, United Kingdom.
authors.forename: Dmitry G
authors.initials: DG
authors.lastname: Revin
authors.affiliation: Department of Physics and Astronomy, University of Sheffield, Hounsfield Road, Sheffield S3 7RH, United Kingdom.
authors.forename: Shiyong Y
authors.initials: SY
authors.lastname: Zhang
authors.affiliation: Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, United Kingdom. Electronic address: a.m.sanchez@warwick.ac.uk.
authors.forename: Ana M
authors.initials: AM
authors.lastname: Sanchez
keywords: Geometric phase analysis (GPA); Interfaces; Scanning transmission electron microscopy (STEM); Strain