title: Imaging screw dislocations at atomic resolution by aberration-corrected electron optical sectioning.
abstract: Screw dislocations play an important role in materials' mechanical, electrical and optical properties. However, imaging the atomic displacements in screw dislocations remains challenging. Although advanced electron microscopy techniques have allowed atomic-scale characterization of edge dislocations from the conventional end-on view, for screw dislocations, the atoms are predominantly displaced parallel to the dislocation line, and therefore the screw displacements are parallel to the electron beam and become invisible when viewed end-on. Here we show that screw displacements can be imaged directly with the dislocation lying in a plane transverse to the electron beam by optical sectioning using annular dark field imaging in a scanning transmission electron microscope. Applying this technique to a mixed [a+c] dislocation in GaN allows direct imaging of a screw dissociation with a 1.65-nm dissociation distance, thereby demonstrating a new method for characterizing dislocation core structures.
authors.affiliation: Department of Materials, University of Oxford, 16 Parks Road, Oxford OX1 3PH, UK.
authors.forename: H
authors.identifier: http://orcid.org/0000-0003-2326-7317
authors.initials: H
authors.lastname: Yang
authors.affiliation: Department of Materials, University of Oxford, 16 Parks Road, Oxford OX1 3PH, UK.
authors.forename: J G
authors.initials: JG
authors.lastname: Lozano
authors.affiliation: Department of Materials, University of Oxford, 16 Parks Road, Oxford OX1 3PH, UK.|EPSRC SuperSTEM Facility, STFC Daresbury, WA4 4AD, UK.
authors.forename: T J
authors.initials: TJ
authors.lastname: Pennycook
authors.affiliation: Department of Materials, University of Oxford, 16 Parks Road, Oxford OX1 3PH, UK.
authors.forename: L
authors.identifier: http://orcid.org/0000-0002-6907-0731
authors.initials: L
authors.lastname: Jones
authors.affiliation: Department of Materials, University of Oxford, 16 Parks Road, Oxford OX1 3PH, UK.
authors.forename: P B
authors.initials: PB
authors.lastname: Hirsch
authors.affiliation: Department of Materials, University of Oxford, 16 Parks Road, Oxford OX1 3PH, UK.|EPSRC SuperSTEM Facility, STFC Daresbury, WA4 4AD, UK.
authors.forename: P D
authors.initials: PD
authors.lastname: Nellist