A computational framework based on the differential algebra (DA) method is presented for calculating aberration coefficients up to fifth order in electromagnetic lenses. To bridge discrete numerical field calculations with high-order DA tracking, a local analytical field-fitting method is proposed. The electromagnetic field obtained from finite-element analysis is first decomposed by Fourier analysis, interpolated along the optical axis using linear Lagrange interpolation, and subsequently fitted to the corresponding analytical basis functions through least-squares fitting. The fitted field representations are validated against OPERA FEA results and an AFFs-based method, while the DA aberration calculation program is further verified against COSY INFINITY using ideal models. For practical finite-element models, the two field-representation methods yield generally consistent high-order aberration coefficients. These results demonstrate the applicability of the proposed framework to high-order aberration calculations based on practical finite-element fields.
Scanning Ion Conductance Microscopy (SICM) can realize three-dimensional, non-invasive imaging of living biological cells, and has made significant progress in fields such as cell biology and medicine. However, constrained by the maximum motion range of the piezoelectric actuator (e.g., 100 μm × 100 μm), it always makes high-precision large-scale scanning technically challenging. In order to address this problem, this study proposes a non-linear spatial stitching method for SICM images based on adaptive region candidates. The method selects overlapping regions through the proposed region candidate strategy, then performs secondary scanning, and it uses pixel-level fitting to utilize the features of the overlapping regions. The scanned images are stitched together by using a non-linear spatial image stitching method, which can effectively expand the scanning range of SICM. Experimental results have shown that the proposed method can achieve stitching in three-dimensional topography scanning images of static regular patterns and different samples such as living cells. The structural similarity index of scanned image obtained by the proposed method is 0.927 (the highest), higher than the traditional method. The new method enables SICM to achieve the ability of scanning imaging from cell size to large-scale tissue scanning imaging.
Beam-induced damage fundamentally limits the characterization of beam-sensitive materials by scanning transmission electron microscopy (STEM), since structural information must be recorded before the electron beam irreversibly modifies the specimen. Here, sodium chloride (NaCl) is employed as a model beam-sensitive ionic crystal to investigate beam-induced structural evolution and the low-dose regime in which useful structural information can be recovered prior to significant damage. Four-dimensional STEM (4D-STEM) datasets were acquired at 200 kV using a Timepix3 direct electron detector and reconstructed using real-time integrated centre of mass (riCoM) imaging. We first establish the characteristic damage behavior of NaCl under high electron doses. Across different dwell times and raster scan orientations, damage develops reproducibly into square-faceted voids whose boundaries align with the 100 crystallographic directions of the rock-salt lattice, indicating that the morphology is governed predominantly by the intrinsic crystallography rather than the scan geometry. We then investigate the low-dose imaging regime using dose-fractionated acquisitions. At 130 e-A-2 per frame, normalized cross-correlation with respect to the first frame quantitatively tracks progressive structural degradation and enables the onset of measurable damage to be identified as a function of accumulated dose. A subsequent acquisition at 32 e-A-2 per frame demonstrates that atomic-scale spatial information can still be recovered below this damage threshold. These results demonstrate how dose-efficient 4D-STEM acquisition combined with riCoM imaging can extend the accessible imaging regime of highly beam-sensitive ionic materials while preserving atomic-scale information.
