Atomic‐Scale Surface Imaging of Bulk Epitaxial CsPbBr ₃ Perovskite Single Crystals on Mica Using Light Assisted Scanning Tunneling Microscopy at Low‐Temperature (80 K)

Epitaxial single‐crystalline CsPbBr 3 perovskite films on mica, prepared ex situ, are explored using a low‐temperature scanning tunneling microscope (STM) by probing the unoccupied electronic states of their surface in ultra‐high vacuum (UHV) at 80 K. Light‐assisted STM measurements under a broadband illumination with visible light were employed to enhance and stabilize surface conductivity. STM imaging across the surface of macroscopic bulk CsPbBr 3 films reveals large flat terraces characterized by a specific type of surface reconstruction, consisting of parallel rows of U‐shaped atomic nanostructures. These structures are spaced by 12 Å and exhibit an internal feature size of 5.1 Å. Density functional theory (DFT) calculations reproduce the experimental observations and reveal a competition between different orthorhombic CsPbBr 3 (110) surface reconstructions: a Cs‐rich structure, identified as the most energetically stable, and three alternative Pb–Br‐rich reconstructions, which are slightly higher in energy yet remain consistent with the STM data. Additional analyses that explicitly account for the mica substrate exclude the cubic CsPbBr 3 phase and other orthorhombic surface orientations, while showing that variations in the mica surface termination do not alter the preferred CsPbBr 3 (110) reconstruction. This combined approach thereby confirms our assignment and resolves previous STM interpretations of CsPbBr 3 .