Local-orbital Ptychography for Ultrahigh-Resolution Imaging

Technical advances paired with developments in methodology have enabled electron microscopy to reach atomic resolution. Further improving the information limit in microscopic imaging requires further improvements in methodology. Here we report a ptychographic method that describes the object as the sum of discrete atomic-orbital-like functions (for example, Gaussian functions) and the probe in terms of aberration functions. Using this method, we realize an improved information limit of microscopic imaging, reaching down to 14 pm. High-quality probes and objects contribute to superior signal-to-noise ratios at low electron doses, allowing for relaxation of the sample thickness restriction to 50 nm for dense materials. Additionally, our method has the capability to decompose the total phase into element components, revealing that the information limit is element dependent. With enhanced spatial resolution, signal-to-noise ratio and thickness threshold compared with conventional ptychography methods, our local-orbital ptychography may find applications in atomic-resolution imaging of metals, ceramics, electronic devices or beam-sensitive material. Ptychography is a coherent diffractive imaging method that enables atomic resolution in four-dimensional scanning transmission electron microscopy. Taking advantage of the nature of the investigated object, and therefore using atomic-orbital-like functions for the reconstruction of the object, the resolution can be further improved to an information limit of 14 pm.