Understanding how atomic-scale structure governs material functionality is a central challenge across physics, chemistry, and materials science. From batteries to superconductors and quantum materials, many important properties emerge from subtle structural motifs involving light elements, point defects, and local ordering. Despite remarkable advances in electron microscopy, these features often remain difficult to access because of weak scattering contrast and, in many cases, severe electron-beam damage. In this seminar, I will present recent developments in four-dimensional scanning transmission electron microscopy (4D-STEM), with a particular focus on multislice electron ptychography (MEP). By exploiting the rich information encoded in diffraction data and inversely solving the multiple electron scattering, MEP enables quantitative three-dimensional imaging of materials with unprecedented sensitivity to both light and heavy elements. I will show how this approach reveals previously inaccessible atomic-scale phenomena, including local variations in hydrogen concentration within metal hydrides and hidden ordering of oxygen point defects in nickelate superconductors. These studies illustrate how subtle structural inhomogeneities can govern emergent material properties and demonstrate the growing capability of electron microscopy to quantify complex atomic arrangements. I will also discuss our recent efforts to extend MEP to cryogenic temperatures, enabling direct visualization of structural and charge orders near phase transitions. Finally, I will outline future opportunities for pushing electron microscopy beyond structural imaging toward the quantitative mapping of electromagnetic fields and spin textures at the atomic scale.
