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Contrast transfer and noise considerations in focused-probe electron ptychography

DOI: 10.1016/j.ultramic.2020.113189 DOI Help

Authors: Colum M. O'leary (University of Oxford) , Gerardo T. Martinez (University of Oxford) , Emanuela Liberti (Diamond Light Source; University of Oxford) , Martin J. Humphry (Phase Focus Ltd) , Angus I. Kirkland (University of Oxford; Diamond Light Source; The Rosalind Franklin Institute) , Peter D. Nellist (University of Oxford)
Co-authored by industrial partner: Yes

Type: Journal Paper
Journal: Ultramicroscopy , VOL 221

State: Published (Approved)
Published: February 2021
Diamond Proposal Number(s): 20431 , 22317

Abstract: Electron ptychography is a 4-D STEM phase-contrast imaging technique with applications to light-element and beam-sensitive materials. Although the electron dose (electrons incident per unit area on the sample) is the primary figure of merit for imaging beam-sensitive materials, it is also necessary to consider the contrast transfer properties of the imaging technique. Here, we explore the contrast transfer properties of electron ptychography. The contrast transfer of focused-probe, non-iterative electron ptychography using the single-side-band (SSB) method is demonstrated experimentally. The band-pass nature of the phase-contrast transfer function (PCTF) for SSB ptychography places strict limitations on the probe convergence semi-angles required to resolve specific sample features with high contrast. The PCTF of the extended ptychographic iterative engine (ePIE) is broader than that for SSB ptychography, although when both high and low spatial frequencies are transferred, band-pass filtering is required to remove image artefacts. Normalisation of the transfer function with respect to the noise level shows that the transfer window is increased while avoiding noise amplification. Avoiding algorithms containing deconvolution steps may also increase the dose-efficiency of ptychographic phase reconstructions.

Journal Keywords: Focused-probe electron ptychography; Single side-band method; Contrast transfer function

Subject Areas: Technique Development, Physics

Diamond Offline Facilities: Electron Physical Sciences Imaging Centre (ePSIC)
Instruments: E02-JEM ARM 300CF