title: Efficient phase contrast imaging in STEM using a pixelated detector. Part 1: experimental demonstration at atomic resolution.
abstract: We demonstrate a method to achieve high efficiency phase contrast imaging in aberration corrected scanning transmission electron microscopy (STEM) with a pixelated detector. The pixelated detector is used to record the Ronchigram as a function of probe position which is then analyzed with ptychography. Ptychography has previously been used to provide super-resolution beyond the diffraction limit of the optics, alongside numerically correcting for spherical aberration. Here we rely on a hardware aberration corrector to eliminate aberrations, but use the pixelated detector data set to utilize the largest possible volume of Fourier space to create high efficiency phase contrast images. The use of ptychography to diagnose the effects of chromatic aberration is also demonstrated. Finally, the four dimensional dataset is used to compare different bright field detector configurations from the same scan for a sample of bilayer graphene. Our method of high efficiency ptychography produces the clearest images, while annular bright field produces almost no contrast for an in-focus aberration-corrected probe.
authors.affiliation: EPSRC SuperSTEM Facility, Daresbury Laboratory, Warrington WA4 4AD, UK; Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK. Electronic address: tpennycook@gmail.com.
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Pennycook
authors.affiliation: Oak Ridge National Laboratory, Materials Science and Technology Division, Oak Ridge, TN 37830, USA.
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Lupini
authors.affiliation: Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK.
authors.forename: Hao
authors.initials: H
authors.lastname: Yang
authors.affiliation: Nion Co., 1102 8th St., Kirkland, WA 98033, USA.
authors.forename: Matthew F
authors.initials: MF
authors.lastname: Murfitt
authors.affiliation: Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK.
authors.forename: Lewys
authors.initials: L
authors.lastname: Jones
authors.affiliation: EPSRC SuperSTEM Facility, Daresbury Laboratory, Warrington WA4 4AD, UK; Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK.
authors.forename: Peter D
authors.initials: PD
authors.lastname: Nellist
keywords: ABF; Chromatic aberrations; DPC; Phase contrast; Pixelated detectors; Ptycography; STEM