Atomic structure of PbBr2 thin films on Ag (111)

Abstract

Ultra-thin PbBr2 overlayers on Ag (111) surface have been grown using thermal evaporation (physical vapor deposition) in the coverage range of ∼0.05 monolayers (ML) to ∼ 0.22 ML. The surface structure of these films has been studied by scanning tunneling microscopy, verified by low energy electron diffraction, and simulated using density functional theory. PbBr2 is one of the binary constituents for the growth of CsPbBr3 perovskites and therefore, the growth study of PbBr2 is directly relevant to the growth of the more complex perovskite as segregation of different phases can affect the properties of the material. Atomically resolved images of PbBr2 with a coverage of ∼0.05 ML show randomly scattered areas of Pb adatoms. Increasing PbBr2 to ∼0.16 ML show additional evidence for the dissociation of PbBr2, with separate structures associated with Pb and Br. ∼0.22 ML of PbBr2 results in areas of a well ordered (√3 x √3) R30° reconstruction that has a structure incorporating both elements. This study provides the reference information for the better understanding of CsPbBr3 perovskite thin films grown under similar conditions.