Doping efficiency of single and randomly stacked bilayer graphene by iodine adsorption.

We report on the efficiency and thermal stability of p-doping by iodine on single and randomly stacked, weakly coupled bilayer polycrystalline graphene, as directly measured by photoelectron emission microscopy. The doping results in work function value increase of 0.4-0.5 eV, with a higher degree of iodine uptake by the bilayer (2%) as compared to the single layer (1%) suggesting iodine intercalation in the bilayer. The chemistry of iodine is identified accordingly as I₃^- and I₅^- poly iodide anionic complexes with slightly higher concentration of I₅^- in bilayer than monolayer graphene, likely attributed to differences in doping mechanisms. Temperature dependent in-situ annealing of the doped films demonstrated that the doping remains efficient up to 200 °C. [ABSTRACT FROM AUTHOR]