Crystal structure and self-doping in monolayer 2D Ag intercalated between SiC and graphene: a density functional theory investigation

Monolayer Ag intercalation between SiC and graphene exhibits two distinct structural phases, referred to as Ag₁ and Ag₂. The Ag1 phase features an approximate 1:1 Ag-to-SiC ratio and displays surface reconstruction in scanning tunneling microscopy (STM), although its precise atomic configuration has remained unclear. The structure of the Ag₂ phase, which has a higher Ag areal density, has also been unresolved. In this work, we identify energetically favorable atomic models for both Ag₁ and Ag₂ phases through first-principles calculations. The proposed structures show excellent agreement with experimental observations from scanning transmission electron microscopy (STEM), low-energy electron diffraction (LEED), and STM. Furthermore, our calculations reveal that, as compared to the semiconducting nature at the 1:1 ratio, the Ag₂ phase exhibits intrinsic self-doping, due to excess Ag atoms within the unit cell.