Effects of two kinds of intercalated In films on quasi-free-standing monolayer graphene formed above SiC(0001)

The effects of In atoms intercalated between the n-type 6H–SiC(0001) substrate and the (63×63)R30∘ zero layer (ZL) on the interface morphology, chemical composition and electron band structure were investigated by scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), core-level/valence-band photoemission spectroscopy (PES) and angle-resolved photoemission spectroscopy (ARPES). As a result of In intercalation, two kinds of ordered In films depending on the thickness of In as well as the annealing temperature were formed under quasi-free-standing monolayer graphene (QFMLG) transformed from ZL. One is a bilayer film, which is stable under 800 °C. The other is a monolayer film composed of In adatoms of a (3×3)R30∘ structure, which survives over 800 °C. The latter induces electron doping of the QFMLG stronger than the former. In addition, the QFMLG on the (3×3)R30∘ film becomes more n-doped under higher annealing temperature, which is due to a vacancy increment of the In film. [Display omitted]