Controlling the electronic structure of graphene using surface-adsorbate interactions

Hybridization of atomic orbitals in graphene on Ni(111) opens a large energy gap of ≈2.8 eV between non-hybridized states at the K-point. Here we use alkali metal adsorbate to reduce and even eliminate this energy gap, and also identify a mechanism responsible for decoupling graphene from the Ni substrate without intercalation of atomic species underneath graphene. Using angle-resolved photoemission spectroscopy and density functional theory calculations, we show that the energy gap is reduced to 1.3 eV due to moderate decoupling after adsorption of Na on top of graphene. Calculations confirm that after adsorption of Na the propensity of graphene bonding to Ni is much lower due to reduced overlap of atomic orbitals, which results from n-doping of graphene. Moreover, we show that the energy gap is eliminated by strong decoupling resulting in a quasi-freestanding graphene, which is achieved by subsequent intercalation of the Na underneath graphene. The ability to partially decouple graphene from a Ni substrate via n-doping (with or without intercalation) suggests that the graphene-to-substrate interaction could be controlled dynamically using light.