A Comparison of a Direct Electron Detector and a High-Speed Video Camera for a Scanning Precession Electron Diffraction Phase and Orientation Mapping

Abstract

Abstract

Fast Pixelated Detectors in Scanning Transmission Electron Microscopy. Part II: Post-Acquisition Data Processing, Visualization, and Structural Characterization

“…Correcting for the overestimation of the electron counts recorded by the Medipix3 by a factor of 4 due to scattering of 200 kV primary electrons between pixels [see McMullan et al (2007) for a discussion], we estimate the dose to be approximately 4.5 × 10 5 e − /nm 2 . While this is above the low-dose regime needed for most soft or beam-sensitive materials of 10 2 -10 5 e − /nm 2 (Yakovlev & Libera, 2008), there is great scope to reduce the dose through reduction in beam current or, as pointed out by MacLaren et al (2020), by increasing the precession rate in other microscopes that support it.…”

“…The standard precession system was modified (MacLaren et al, 2020) to employ a Medipix3 detector instead of a fast video recording of the fluorescent screen using an external CCD camera. This modification enables improved imaging fidelity and efficiency through the higher detective quantum efficiency and the noise-free readout properties of the direct electron counting detector.…”

“…Using an MgO density of 3.58 g/cm 2 (Egerton, 2011), λ is 137 nm, giving the thickness of our MgO sample as 81 nm, sufficiently thick for there to be significant dynamical effects from multiple elastic scattering. The standard precession system was modified (MacLaren et al, 2020) to employ a Medipix3 detector instead of a fast video recording of the fluorescent screen using an external CCD camera. This modification enables improved imaging fidelity and efficiency through the higher detective quantum efficiency and the noise-free readout properties of the direct electron counting detector.…”

“…To demonstrate our technique, we apply it to a commercially available crystalline MgO substrate imaged in a JEOL ARM200cF TEM operated at 200 kV in SPED mode using a custom (MacLaren et al, 2020) DigiSTAR precession system from NanoMEGAS. MgO is a widely studied material (Yang et al, 2006) that is used in magnetic tunnel junctions (Parkin et al, 2004; Zhu & Park, 2006) and is of interest as a room temperature ferromagnetic insulator when strained (Jin et al, 2015).…”

“…Lastly, general lattice image processing is discussed in the section "Lattice analysis", with a focus on diffraction imaging. Using test data obtained in the SPED mode of acquisition (Vincent & Midgley, 1994) of a custom system (MacLaren et al, 2020), we demonstrate that a lattice parameter fractional precision of 6 ×10 −4 is possible using a probe with a spatial resolution of 1.1 nm. This precision value is approximately 2-3× larger than the best ones reported in the literature using standard probes in a SPED mode (Rouvière et al, 2013) and patterned probes in standard STEM mode (Guzzinati et al, 2019;Zeltmann et al, 2020).…”