Atomic-Scale Surface Imaging of bulk Epitaxial CsPbBr3 Perovskite Single Crystals on Mica using Light Assisted Scanning Tunneling Microscopy at Low-Temperature (80 K)

TL;DR

This study employs light-assisted low-temperature STM and DFT calculations to reveal atomic-scale surface structures of bulk CsPbBr3 perovskite crystals on mica, clarifying surface reconstructions and ruling out other phases.

Contribution

It demonstrates the use of light-assisted STM at low temperature combined with DFT to accurately characterize surface reconstructions of epitaxial CsPbBr3 perovskite on mica, resolving previous ambiguities.

Findings

Identification of flat terraces with U-shaped nanostructures

Confirmation of Cs-rich surface reconstruction as most stable

Exclusion of cubic CsPbBr3 phase and other orientations

Abstract

Epitaxial single-crystalline CsPbBr3 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 CsPbBr3 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 angstroms and exhibit an internal periodicity of 5.1 angstroms. Density functional theory (DFT) calculations reproduce the experimental observations and reveal a competition between different orthorhombic CsPbBr3(110) surface reconstructions: a Cs-rich structure, identified as the most energetically stable, and three alternative PbBr 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 CsPbBr3 phase and other orthorhombic surface orientations, while showing that variations in the mica surface termination do not alter the preferred CsPbBr3(110) reconstruction. This combined approach thereby confirms our assignment and resolves previous STM interpretations of CsPbBr3.