Abstract
Interaction of sodium with graphene (Gr) on Ir(111) was studied with the aim to resolve the issue of Na adsorption/intercalation kinetics. The system Na/Gr/Ir(111) was studied by means of angle-resolved photoemission spectroscopy, low-energy electron diffraction, and ab initio density functional theory (DFT) calculation. It has been found that at room temperature (RT) and low concentrations Na is dominantly adsorbed on graphene. At higher concentrations, an intercalation process sets in so that it is possible to observe the coexistence of these two states. Eventually, all Na atoms are found in the intercalated state as determined by exposure to oxygen. While adsorption of Na on graphene already intercalated by Na [Na/Gr/Na/Ir(111) system] at RT was not possible, we could observe Li adsorption through the increase of Dirac point binding energy. Li coadsorption strongly affects the binding energy of the iridium surface state as well. This finding was supported by DFT calculations of adsorption energy of Na and Li on bare and fully Na intercalated graphene.
Highlights
Despite the extraordinary physical properties of graphene, there are several reasons why, from the early days of graphene research, scientists have been trying to alter its structural and electronic properties [1] as well as its interaction with the supporting surfaces [2,3,4]
It has been demonstrated that adsorption and/or intercalation of alkali metals (AMs) could be successfully used to modify the charge-carrier density in graphene, manipulate its electronic structure [8,9], and thereby alter its chemical reactivity [10,11,12]
A recent density functional theory (DFT) study of AM adsorption/intercalation on graphene supported by the Au/Ni(111) substrate showed a substantially larger binding energy of all AM in the intercalated state than in the adsorbed state [36]
Summary
Despite the extraordinary physical properties of graphene, there are several reasons why, from the early days of graphene research, scientists have been trying to alter its structural and electronic properties [1] as well as its interaction with the supporting surfaces [2,3,4]. A doping-induced shift of the Dirac point to higher binding energies is usually associated with the band renormalization just below the Fermi level which, in turn, is due to the electron-phonon coupling (EPC) [16,19].
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