Polymorphic Phases of Metal Chlorides in the Confined 2D Space of Bilayer Graphene

Unprecedented two-dimensional (2D) metal chloride structures were grown between sheets of bilayer graphene through intercalation of metal and chlorine atoms. Numerous spatially confined 2D phases of AlCl3 and CuCl2 distinct from their typical bulk forms were found, and the transformations between these new phases under the electron beam were directly observed by in situ scanning transmission electron microscopy (STEM). Our density functional theory calculations confirmed the metastability of the atomic structures derived from the STEM experiments and provided insights into the electronic properties of the phases, which range from insulators to semimetals. Additionally, the co-intercalation of different metal chlorides was found to create completely new hybrid systems; in-plane quasi-1D AlCl3/CuCl2 heterostructures were obtained. The existence of polymorphic phases hints at the unique possibilities for fabricating new types of 2D materials with diverse electronic properties confined between graphene sheets.