Efficient phase contrast imaging in STEM using a pixelated detector. Part 1: experimental demonstration at atomic resolution

Timothy J Pennycook; Andrew R Lupini; Hao Yang; Matthew F Murfitt; Lewys Jones; Peter D Nellist

doi:10.1016/j.ultramic.2014.09.013

Efficient phase contrast imaging in STEM using a pixelated detector. Part 1: experimental demonstration at atomic resolution

Ultramicroscopy. 2015 Apr:151:160-167. doi: 10.1016/j.ultramic.2014.09.013. Epub 2014 Oct 15.

Authors

Timothy J Pennycook¹, Andrew R Lupini², Hao Yang³, Matthew F Murfitt⁴, Lewys Jones³, Peter D Nellist⁵

Affiliations

¹ 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.
² Oak Ridge National Laboratory, Materials Science and Technology Division, Oak Ridge, TN 37830, USA.
³ Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK.
⁴ Nion Co., 1102 8th St., Kirkland, WA 98033, USA.
⁵ EPSRC SuperSTEM Facility, Daresbury Laboratory, Warrington WA4 4AD, UK; Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK.

PMID: 25458189
DOI: 10.1016/j.ultramic.2014.09.013

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.

Keywords: ABF; Chromatic aberrations; DPC; Phase contrast; Pixelated detectors; Ptycography; STEM.

Publication types

Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, Non-P.H.S.