Measuring nanometre-scale electric fields in scanning transmission electron microscopy using segmented detectors

• Published in: Ultramicroscopy Vol. 182; pp. 169 - 178
• Main Authors: Brown, H.G., Shibata, N., Sasaki, H., Petersen, T.C., Paganin, D.M., Morgan, M.J., Findlay, S.D.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01-11-2017
• Subjects: Differential phase contrast (DPC) imaging; Electric fields; p-n junctions; Scanning transmission electron microscopy (STEM); p-n junctions; Scanning transmission electron microscopy (STEM); Differential phase contrast (DPC) imaging; Electric fields
• ISSN: 0304-3991; 1879-2723
• DOI: 10.1016/j.ultramic.2017.07.002

•Differential phase contrast (DPC) and two ptychography variants are compared.•All systematically underestimate the beam deflection and thus the electric field.•In DPC, correction via a calibration experiment gives quantitatively good results.•In ptychography, a correction for plasmon scattering improves the reconstruction.•We discuss a refinement for handling reconstruction of non-periodic objects.
Electric field mapping using segmented detectors in the scanning transmission electron microscope has recently been achieved at the nanometre scale. However, converting these results to quantitative field measurements involves assumptions whose validity is unclear for thick specimens. We consider three approaches to quantitative reconstruction of the projected electric potential using segmented detectors: a segmented detector approximation to differential phase contrast and two variants on ptychographical reconstruction. Limitations to these approaches are also studied, particularly errors arising from detector segment size, inelastic scattering, and non-periodic boundary conditions. A simple calibration experiment is described which corrects the differential phase contrast reconstruction to give reliable quantitative results despite the finite detector segment size and the effects of plasmon scattering in thick specimens. A plasmon scattering correction to the segmented detector ptychography approaches is also given. Avoiding the imposition of periodic boundary conditions on the reconstructed projected electric potential leads to more realistic reconstructions.