Hydrogen intercalation of graphene grown on 6H-SiC(0001)

Atomic hydrogen exposures on a monolayer graphene grown on the SiC(0001) surface are shown to result in hydrogen intercalation. The hydrogen intercalation induces a transformation of the monolayer graphene and the carbon buffer layer to bi-layer graphene without a buffer layer. The STM, LEED, and core-level photoelectron spectroscopy measurements reveal that hydrogen atoms can go underneath the graphene and the carbon buffer layer and bond to Si atoms at the substrate interface. This transforms the buffer layer into a second graphene layer. Hydrogen exposure results initially in the formation of bi-layer graphene islands on the surface. With larger atomic hydrogen exposures, the islands grow in size and merge until the surface is fully covered with bi-layer graphene. A 3 × 3 R 30 ∘ periodicity is observed on the bi-layer areas. ARPES and energy filtered XPEEM investigations of the electron band structure confirm that after hydrogenation the single π-band characteristic of monolayer graphene is replaced by two π-bands that represent bi-layer graphene. Annealing an intercalated sample, representing bi-layer graphene, to a temperature of 850 °C, or higher, re-establishes the monolayer graphene with a buffer layer on SiC(0001).