Seminar: Alexis Wartelle, Institut Néel

The ongoing efforts to design smaller and more efficient electronic components have emphasized a need for reliable and quantitative measurements of electric fields down to the nanoscale. In this respect, the small-diameter electron beams available in Scanning Transmission Electron Microscopy (STEM) are close to the ideal probe. Since electric fields cause them to undergo an angular deflection, the challenge consists in a precise measurement of this angle across the sample of interest. This task is now within reach, thanks to the advent of fast and pixelated direct electron detectors, which enable an accurate "angular tracking" of the beam over a sample region. As the datasets are 2D images (detector frames) acquired on a 2D map of the sample, this kind of experiment falls into the field called "4D-STEM". In this presentation, I will start from the conventional, center-of-mass approach to extracting electric fields from 4D-STEM data. Some results obtained with Institut Néel's new TEM (Jeol NeoArm) will be described. Another data processing path, namely template matching (i.e. image registration), will be discussed along with a recent investigation of its sensitivity to aberrations in the electron probe. As an outlook, I will try to make a case for electron ptychography.