Raman Response of Monolayer Graphene Upon Varying TCNE Adsorption

ABSTRACT Graphene is the prototype two‐dimensional material with an intriguing Dirac‐like electronic dispersion relation. To control graphene's material properties, the non‐covalent adsorption of molecular species remains a promising approach and has been proven to have high potential due to the vast pool of available molecules. However, loading of graphene with molecules can come at the expense of breaking translational lattice symmetry locally, traceable by the D‐band emergence in the Raman spectrum. This implies that new scattering channels of charge carriers between the nonequivalent sites in the Brillouin zone of graphene occur, detrimental to the overall electronic properties of graphene. Instead, an ideal molecular dopant should modify the electronics of graphene while being lattice‐symmetry preserving. We report that TCNE adsorbed on graphene in the low loading limit does not compel a significant D‐band emergence while simultaneously acting as a sizable p‐type dopant. This remarkable property of TCNE can be rationalized by considering its high‐symmetry adsorption sites on graphene. The findings identify TCNE as a highly suitable molecule for opening a broader scope of application fields ranging from classical charge carrier density control to more fundamental and quantum‐related steering of properties.