Visualization of electric fields using electron scattering

Aberration-corrected Annular Dark Field STEM (ac-ADF-STEM) has provided some beautiful images and valuable insights into materials such as semiconductors, with each atom clearly resolved. New developments in fast pixelated detectors now allow a four-dimensional (4D) dataset to be acquired, where for each position of the electron probe, scanned in a 2D raster over the sample, a 2D image of the diffraction plane is recorded. This 4D-STEM data is useful because scientifically interesting signals, such as the presence of an internal electric field, exist in electron scattering patterns as second-order effects that are missed by an averaging detector but are very accessible when the complete data are collected. An electric field changes the trajectory of the electron beam due to the Lorentz force. The deflection of the electron beam is magnified by post-specimen lenses. The ability of 4D-STEM to measure internal fields in a device structure without the need for contacts is extremely useful and could be applied for example to measure the electric field in advanced functional materials. The capability in hardware, software and methods that will be developed will allow live imaging of internal electric fields at length scales from microns to atomic resolution.