Understanding how materials form and combine with one another is important to design better energy-harvesting and -storage devices. Now, researchers have directly imaged the loss of a single layer of atoms in a photocatalyst created by layering two oxides. The team examined the structure of a single layer and that of the final composite, finding that a plane of atoms right at the material boundary was lost during the synthesis process. The team showed that the starting material’s surface is unstable and can dramatically reconfigure when combined with a second layer.