Suppressing dynamical diffraction artefacts in differential phase contrast scanning transmission electron microscopy of long-range electromagnetic fields via precession

• Published in: Ultramicroscopy Vol. 219; p. 113097
• Main Authors: Mawson, T., Nakamura, A., Petersen, T.C., Shibata, N., Sasaki, H., Paganin, D.M., Morgan, M.J., Findlay, S.D.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.12.2020
• Subjects: Differential phase contrast; Dynamical diffraction; Precession; Scanning transmission electron microscopy; Differential phase contrast; Precession; Dynamical diffraction; Scanning transmission electron microscopy
• ISSN: 0304-3991; 1879-2723
• DOI: 10.1016/j.ultramic.2020.113097

•Dynamical electron diffraction complicates electromagnetic field mapping via DPC.•Diffraction artefacts from sample bending & thickness variation studied in simulation.•Effects most pronounced in thick (several 10s to 100s of nanometers) samples.•A metric is introduced for the scale of these diffraction artefacts.•Precession by a few milliradian can suppress such artefacts by an order of magnitude. It is well known that dynamical diffraction varies with changes in sample thickness and local crystal orientation (due to sample bending). In differential phase contrast scanning transmission electron microscopy (DPC-STEM), this can produce contrast comparable to that arising from the long-range electromagnetic fields probed by this technique. Through simulation we explore the scale of these dynamical diffraction artefacts and introduce a metric for the magnitude of their contribution to the contrast. We show that precession over an angular range of a few milliradian can suppress this contribution to the contrast by one-to-two orders of magnitude. Our exploration centres around a case study of GaAs near the [011] zone-axis orientation using a probe-forming aperture semiangle on the order of 0.1 mrad at 300 keV, but the trends found and methodology used are expected to apply more generally.