Disorder beneath epitaxial graphene on SiC(0001): An x-ray absorption study

Abstract

The evolution of silicon carbide (0001) surface reconstruction upon annealing has been studied by SiK -edge near-edge x-ray-absorption fine structure (NEXAFS). With the increase in annealing temperature, the fluorescence yield of SiK -edge NEXAFS clearly indicates an increase in disorder of Si atoms in the much deeper interior beneath the surface due to out diffusion of Si atoms to the surface forming increased Si vacancies. The concentration of Si vacancies beneath the epitaxial graphene formed by high-temperature annealing of SiC is estimated to be as high as 15% to a depth of several micrometers. As acceptors in SiC, the high concentration of Si vacancies could have a significant impact on the electronic properties of epitaxial graphene by charge-transfer doping from the substrate and the introduction of interface states. © 2008 The American Physical Society.