Abstract:

Epitaxial graphene layers were successfully grown onto Si-terminated 6H-SiC(0001) substrates by thermal annealing using an ultrahigh vacuum molecular beam epitaxy(MBE) chamber. The morphology and  structure of the samples annealed for different time were characterized by reflection high energy diffraction (RHEED), Raman spectroscopy, atomic force microscopy (AFM) and near edge X-ray absorption fine structure spectroscopy (NEXAFS). The graphene diffraction steaks were found in the RHEED patterns for all samples. AFM results showed that as the annealing time increased, the thickness of the graphene layers increased and the surface morphology appeared smoother with the out-of-order voids reduced. Raman results showed that the G peak and the 2D peak of graphene were obviously blue-shifted compared to those of highly-oriented pyrolytic graphite (HOPG). At longer annealing time, the amount of blue-shift decreased. C K-edge NEXAFS results revealed that the intensity of the resonance absorption peaks for 1s→π and 1s→σ for the sp2 hybridized C atoms increased when the samples were annealed over longer periods. The 1s→π peaks of these samples were at higher energies compared to those of HOPG.

Key words: Raman, Graphene, 6H-SiC, Annealing time, RHEED, AFM, NEXAFS