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1. Design of Electrostatic Aberration Correctors for Scanning Transmission Electron Microscopy

   Ribet, S. (January 2023, Condensed matter)

   In a scanning transmission electron microscope (STEM), producing a high-resolution image generally requires an electron beam focused to the smallest point possible. However, the magnetic lenses used to focus the beam are unavoidably imperfect, introducing aberrations that limit resolution. Modern STEMs overcome this by using hardware aberration correctors comprised of many multipole lenses, but these devices are complex, expensive, and can be difficult to tune. We demonstrate a design for an electrostatic phase plate that can act as an aberration corrector. The corrector is comprised of annular segments, each of which is an independent two-terminal device that can apply a constant or ramped phase shift to a portion of the electron beam. We show the improvement in image resolution using an electrostatic corrector. Engineering criteria impose that much of the beam within the probe-forming aperture be blocked by support bars, leading to large probe tails for the corrected probe that sample the specimen beyond the central lobe. We also show how this device can be used to create other STEM beam profiles such as vortex beams and beams with a high degree of phase diversity, which improve information transfer in ptychographic reconstructions. 

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2. PtyRAD: A High-Performance and Flexible Ptychographic Reconstruction Framework with Automatic Differentiation

   https://doi.org/10.1093/mam/ozaf070  

   Lee, Chia-Hao; Zeltmann, Steven E; Yoon, Dasol; Ma, Desheng; Muller, David A (July 2025, Microscopy and Microanalysis)

   Abstract Electron ptychography has recently achieved unprecedented resolution, offering valuable insights across diverse material systems, including in three dimensions. However, high-quality ptychographic reconstruction is computationally expensive and time consuming, requiring a significant amount of manually tuning even for experts. Additionally, essential tools for ptychographic analysis are often scattered across multiple software packages, with some advanced features available only in costly commercial software like MATLAB. To address these challenges, we introduce PtyRAD (Ptychographic Reconstruction with Automatic Differentiation), an open-source software framework offers a comprehensive, flexible, and computationally efficient solution for electron ptychography. PtyRAD provides seamless optimization of multiple parameters—such as sample thickness, local tilts, probe positions, and mixed probe and object modes—using gradient-based methods with automatic differentiation. By utilizing PyTorch’s highly optimized tensor operations, PtyRAD achieves up to a 24× speedup in reconstruction time compared to existing packages without compromising image quality. In addition, we propose a real-space depth regularization, which avoids wrap-around artifacts and can be useful for twisted two-dimensional material datasets and vertical heterostructures. Moreover, PtyRAD integrates a Bayesian optimization workflow that streamlines hyperparameter selection. We hope the open-source nature of PtyRAD will foster reproducibility and community-driven development for future advances in ptychographic imaging. 

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3. Using Aberrations to Improve Dose-Efficient Tilt-corrected 4D-STEM Imaging

   https://doi.org/10.1093/mam/ozag008  

   Ma, Desheng; Muller, David A; Zeltmann, Steven E (March 2026, Microscopy and Microanalysis)

   Abstract Tilt-corrected imaging methods in four-dimensional scanning transmission electron microscopy (4D-STEM) have recently emerged as a new class of direct ptychography methods that are especially useful at low dose. The operation of tilt correction unfolds the contrast transfer functions (CTFs) of the virtual bright-field images and retains coherence by correcting aberration-induced spatial shifts. By performing summation or subtraction of the tilt-corrected images, the real or imaginary parts of the complex phase-contrast transfer functions are recovered, producing a tilt-corrected bright field image (tcBF) or a differential phase contrast image (tcDPC). However, the CTF can be strongly damped by the introduction of higher-order aberrations than defocus. In this paper, we show how aberration-corrected bright-field imaging (acBF), which combines tcBF and tcDPC, enables continuously-nonzero contrast transfer within the information limit, even in the presence of higher-order aberrations. In fact, higher-order aberrations can be beneficial, removing oscillations from the acBF CTF. We demonstrate acBF on both simulated and experimental data, showing it produces superior performance to tcBF or DPC methods alone, and discuss its limitations, including estimates for the number of pixels needed on the detector. 

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4. Detective Quantum Efficiency-Based Comparison of HRTEM and Ptychography Phase Imaging

   https://doi.org/10.1093/mam/ozag018  

   Bennemann, Felix; Kirkland, Angus I; Muller, David A; Nellist, Peter D (March 2026, Microscopy and Microanalysis)

   Abstract High-resolution transmission electron microscopy (HRTEM) is an important method for imaging beam sensitive materials often under cryo conditions. Electron ptychography in the scanning transmission electron microscope (STEM) has been shown to reconstruct low-noise phase data at a reduced fluence for such materials. This raises the question of whether ptychography or HRTEM provides a more fluence-efficient imaging technique. Even though the transfer function is a common metric for evaluating the performance of an imaging method, it only describes the signal transfer with respect to spatial frequency, irrespective of the noise transfer. It can also not be well defined for methods, such as ptychography, that use an algorithm to form the final image. Here we apply the concept of detective quantum efficiency (DQE) to electron microscopy as a fluence independent and sample independent measure of technique performance. We find that, for a weak-phase object, ptychography can never reach the efficiency of a perfect Zernike phase imaging microscope but that ptychography is more robust to partial coherence. 

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5. Ultracold cryogenic TEM with liquid helium and high stability

   https://doi.org/10.1073/pnas.2509736122  

   Rennich, Emily; Sung, Suk Hyun; Agarwal, Nishkarsh; Gates, Maya; Kerns, Robert; Hovden, Robert; Baggari, Ismail El (September 2025, Proceedings of the National Academy of Sciences)

   Davis, JC (Ed.)

   Cryogenic transmission electron microscopy has revolutionized structural biology and materials science. To image below liquid nitrogen temperatures, various liquid helium stages have been constructed but have proven to be complex and unstable, making high-resolution imaging challenging. This problem is even more pronounced in side-entry specimen holders common on modern transmission electron microscopes. Here, we introduce an ultracold liquid helium transmission electron microscope side-entry specimen holder, featuring continuous cryogen flow and vibration decoupling. This instrument is compatible with modern aberration-corrected microscopes and achieves sub-25 K base temperature, +/-2 mK thermal stability over many hours, and atomic resolution—setting the stage for a new era of cryogenic electron microscopy. 

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