Abstract
A reformulated implementation of single-sideband ptychography enables analysis and display of live detector data streams in 4D scanning transmission electron microscopy (STEM) using the LiberTEM open-source platform. This is combined with live first moment and further virtual STEM detector analysis. Processing of both real experimental and simulated data shows the characteristics of this method when data are processed progressively, as opposed to the usual offline processing of a complete data set. In particular, the single-sideband method is compared with other techniques such as the enhanced ptychographic engine in order to ascertain its capability for structural imaging at increased specimen thickness. Qualitatively interpretable live results are obtained also if the sample is moved, or magnification is changed during the analysis. This allows live optimization of instrument as well as specimen parameters during the analysis. The methodology is especially expected to improve contrast- and dose-efficient in situ imaging of weakly scattering specimens, where fast live feedback during the experiment is required.
Highlights
The development of ultrafast cameras for transmission electron microscopy (TEM) such as the pnCCD (Müller et al, 2012; Ryll et al, 2016), the Medipix3 chip (Plackett et al, 2013), delay-line detectors (Oelsner et al, 2001; Müller-Caspary et al, 2015), or the EMPAD (Tate et al, 2016) enabled the collection of the full diffraction space up to a flexible cutoff spatial frequency at each scan point in scanning TEM (STEM)
We demonstrate 4D-scanning transmission electron microscopy (STEM) continuous live scanning with the simultaneous ptychographic single-sideband (SSB) reconstruction combined with bright field, annular dark field, and first moment imaging, including its divergence which is proportional to the charge density in thin specimens
Depending on the model presumed for the interaction between specimen and incident STEM probe, the direct inversion of the data can either be done by Wigner Distribution Deconvolution (WDD) or the SSB ptychography scheme (Rodenburg et al, 1993)
Summary
The development of ultrafast cameras for transmission electron microscopy (TEM) such as the pnCCD (Müller et al, 2012; Ryll et al, 2016), the Medipix chip (Plackett et al, 2013), delay-line detectors (Oelsner et al, 2001; Müller-Caspary et al, 2015), or the EMPAD (Tate et al, 2016) enabled the collection of the full diffraction space up to a flexible cutoff spatial frequency at each scan point in scanning TEM (STEM). It achieves a better signal-to-noise ratio for weak phase objects than annular bright field or differential phase contrast (Seki et al, 2018) and allows reconstruction at extremely low dose (O’Leary et al, 2020)
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