Epitaxial graphene on<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mn>6</mml:mn><mml:mi>H</mml:mi><mml:mtext>-SiC</mml:mtext></mml:mrow></mml:math>and Li intercalation

The influence of lithium (Li) exposures on monolayer graphene grown on the silicon-terminated SiC(0001) surface is investigated using low-energy electron microscopy, photoelectron spectroscopy, and micro-low-energy electron diffraction. After Li deposition, islands or Li droplets are observed on the surface, and are found to coalesce together with time. Formation of a dipole layer at the interface, interpreted to originate from Li-Si bonding, is observed directly after Li deposition, and manifested by a 2 eV shift of the $\text{C}\text{ }1s$ and $\text{Si}\text{ }2p$ bulk SiC peaks. This indicates that Li atoms penetrate through the graphene and carbon buffer layer directly after deposition at room temperature since three $\ensuremath{\pi}$ bands are then moreover observed at the K point, instead of the single $\ensuremath{\pi}$ band for monolayer graphene. The existence of three $\ensuremath{\pi}$ bands is interpreted as a mixture of bilayer and monolayer graphene plus a difference in doping levels due to an uneven distribution of Li atoms. Li gives rise to electron doping of the graphene and results in a lowering of the Dirac point. After annealing to a few hundred degrees Celsius, a more even Li distribution and intercalation is obtained since then two distinct $\ensuremath{\pi}$ bands appear at the K point.