STM study of oxygen intercalation at the graphene/Ni(111) interface
This paper reports an STM study of all stages of the intercalation of oxygen at the interface of a strongly coupled graphene/Ni(111) system prepared by temperature programmed growth (TPG) method. We have found that at the first stage of the intercalation at 120 °C, oxygen forms a chemisorbed layer on Ni(111) with a coverage about 0.26–0.28 ML, approximately described by the compressed p(2×2) lattice. The second stage of the intercalation is the formation of a single NiO(100) layer visualized in STM images as a specific ’square’ superstructure at the graphene/Ni(111) interface. It was also established that the rate of the oxygen intercalation at 250 °C is much higher than at 120 °C. After intercalation at 250 °C, STM also reveals the formation of regions with ’free-standing’ graphene, associated with the presence of a double nickel oxide layer underneath.