Variable electric field gating of hexagonal boron nitride monolayer on Ir(111) by sequential lithium deposition.

Stepwise deposition of Li atoms onto hexagonal boron nitride (hBN) monolayer on Ir(111) is investigated by means of valence-band photoemission spectroscopy and low-energy electron diffraction. Sequential Li deposition progressively shifts the band structure of hBN to higher binding energies due to the induction of a variable electric field originating from electronic charge donation by alkali atoms. At small coverages, Li atoms preferably intercalate under the hBN layer, where they are highly charged and give rise to a large initial shift of the band structure. Additionally, intercalated Li atoms effectively decouple hBN from the substrate and consequently reduce its moire corrugation. As the deposition progresses further, Li atoms also adsorb on top of hBN, and the average charge of both intercalated and adsorbed Li atoms progressively diminishes due to the Coulomb repulsion penalty. This gives rise to a saturation of the respective electric field and the band structure shift, and elaborates on the pathways and limitations of chemical functionalization of epitaxial hBN systems with charge donating species.