Substitutional doping of Ag into epitaxial graphene on 6H-SiC substrates during thermal decomposition

Controllable and damage-free doping of graphene is challenging because of the ultra-thin nature of graphene. In this work, epitaxial graphene prepared by thermal decomposition of 6H-SiC is doped with Ag substitutionally by annealing in a silver atmosphere. Scanning tunneling microscopy (STM) reveals that the Ag atoms are preferentially embedded in the bilayer regions substituting for C atoms at the α sites in the bottom lattice with negligible distortion, and first-principles calculation reveals a thermodynamically stable configuration. Essentially, the Ag atoms penetrate the edges or defects in the top graphene into the buffer layer and participate in crystallization of the second graphene layer during annealing. In this way, Ag atoms are introduced into the graphene lattice substitutionally via covalent bonding with carbon atoms. In addition, hybridization of the C 2p and Ag 4d orbitals results in the asymmetrical distributions of spin-up and spin-down channels and a magnetic moment of 1.06 μ_B emerges for each substitutional Ag. This simple doping approach can be utilized to tune the magnetic properties of graphene.