Differential phase-contrast microscopy at atomic resolution

Differential phase-contrast (DPC) imaging enhances the image contrast of weakly absorbing, low-atomic-number objects in optical and X-ray microscopy(1-4). In transmission electron microscopy(5), this same imaging mode can image magnetic fields in magnetic materials at medium resolution(6,7). Atomic-resolution imaging of electromagnetic fields, however, is still a major challenge. Here, we demonstrate atomic-resolution DPC imaging of crystals using aberration-corrected scanning transmission electron microscopy. The image contrast reflects the gradient of the electrostatic potential of the atoms; that is, the atomic electric field, which is found to be sensitive to the crystal ionicity. Both the mesoscopic polarization fields within each domain and the atomic-scale electric fields induced by the individual electric dipoles within each unit cell can be sensitively detected in ferroelectric BaTiO3. The realization of atomic-resolution DPC microscopy opens a new dimension of microscopy from crystalline materials through to biological molecules.