This article presents a novel approach to achieving sub-ångström resolution in a scanning electron microscope (SEM) using ptychography at 20 keV. Ptychography is a powerful technique that reconstructs high-resolution images by analyzing 2D diffraction data from multiple overlapping sample illumination areas. The authors demonstrate that by using a low-energy electron beam (20 keV) and a non-aberration-corrected SEM, they can achieve a resolution of at least 67 pm, which is a factor of 8.9 improvement over the Abbe resolution limit. This achievement is significant because it challenges the conventional belief that aberration correction and high-energy electron beams are necessary for sub-ångström resolution in electron microscopy.
The study highlights the importance of data diversity in ptychography, as the authors used a CFEG SEM with an immersion objective lens and a low-energy-optimized hybrid direct electron detector. They also developed a method to accurately determine and correct for distortion in collected diffraction data, which is crucial for achieving high resolution. The authors emphasize the potential of this approach for in situ atomic-scale investigations and the structural determination of low-mass proteins, offering a more accessible and cost-effective alternative to conventional high-energy TEMs.
The article provides a detailed experimental setup, including the use of a projector lens, a hybrid-type pixel array direct electron detector, and a method for diffraction data distortion correction. The authors present a comparison between experimental and simulated reconstructions, demonstrating the capability of ptychography to yield information beyond the Abbe resolution limit. The study also discusses the challenges and limitations of the method, such as the need for careful sample preparation and the potential for phase reconstruction ambiguities with thicker samples.
In summary, this research showcases the potential of ptychography in SEM to achieve sub-ångström resolution at a lower beam energy, opening up new possibilities for various applications in materials science, biology, and nanotechnology.
