Prize Talk: Joseph F. Keithley Award For Advances in Measurement*

Electron microscopes use electrons with wavelengths of a few picometers and are potentially capable of imaging individual atoms in solids at a resolution ultimately set by the atoms themselves. Even with the development of aberration-corrector technology the best achievable resolution was more than an order magnitude worse than this, limited by both residual aberrations in the electron lenses and multiple scattering of the incident beam inside the sample. However, with recent advances in detector technology [1] to collect all scattered electrons and ptychographic algorithms to unscramble their multiple scattering, the resolution of the electron microscope is now limited only by the dose to the sample, and thermal vibrations of the atoms themselves.  At high doses, these approaches have allowed us to image the detailed vibrational envelopes of individual atom columns [2].   Solving the multiple scattering problem also recovers three-dimensional information about the sample, including surface relaxations and revealing interstitial dopant atoms that would be hidden by channeling of the probe with conventional imaging modes.  Even the location of all atoms in thin amorphous films now seems within reach. These approaches have also allowed us to image the internal structures of both magnetic and ferroelectric vortices, skyrmions and merons, including their singular points that are critical for accurately describing the topological properties of these field textures.  The reduced sensitivity to chromatic aberrations also makes these ptychographic approaches of interest for thick biological samples.  However, as the dose is reduced, so is our ability to robustly reconstruct the object. Challenges in characterizing and predicting performance will be discussed.