Atomic resolution imaging of light elements in low-dimensional materials

The microscopic world at the atomic scale seems very remote from our daily lives. Still, we exploit exactly this world in our everyday technology like smartphones, batteries and solar cells, which rely on materials with controlled nanometer and atomic scale structures. To keep advancing such technologies it is therefore essential to understand how and why things happen at these small length scales. Despite that the most advanced electron microscopes can image the atomic structure of practically all materials, conventional imaging techniques lack the sensitivity to robustly image light atoms next to heavy ones. Consequently, a large class of materials containing both light and heavy atoms remains unexplored at the atomic scale.This thesis is dedicated to the atomic resolution imaging of light elements next to heavy ones in technologically relevant materials, by using a new sensitive imaging technique, called integrated differential phase contrast, in a scanning transmission electron microscope. Movies of light atoms and their motion in a two-dimensional material are recorded, which reveal the atom-by-atom evolution of defect structures, and also enabled the quantification of radiation damage caused by collisions with the fast primary electrons. Finally, the ultimate imaging sensitivity is demonstrated by imaging hydrogen atoms (the lightest element in the universe) in titanium. Overall, this thesis demonstrates that the entire periodic table is now territory of the electron microscope, which enables research of previously unexplored materials systems containing light elements, which may lead to crucial insights in the physics and chemistry of materials that contribute to technological advancement.