Fig. 1: SEM beam formation and DeepFocus algorithm.
From: DeepFocus: fast focus and astigmatism correction for electron microscopy
a Schematic of the electron beam and the parameters that are controlled by DeepFocus. b Defocus - and astigmatism series (n = 1) that shows the influence of mild working distance (top row: 0 to 8 µm) and stigmator changes (bottom row: 0 to 5 a.u.) on image quality for a Zeiss Merlin SEM with 800 ns dwell time and 10 nm pixel size. Scale bar is 500 nm. c The out-of-focus image (example resolution 1024 × 768, 10 nm pixel size) is perturbed (symmetric perturbation σwd = ±5 µm) and randomly located patch pairs (shared offset within image pair, e.g. blue and pink squares with shape 512 × 512) of fixed shape are cropped and processed by DeepFocus - an artificial neural network consisting of an image encoder and a regression head. A definable number of independent predictions is used to calculate a correction term ΔF for each focus parameter (wd: working distance, stig x: stigmator x; stig y: stigmator y). All SEM images have 10 nm pixel size. Scale bar in b is 500 nm.
