▎ 摘　　要

The continuous improvement of the sublimation process of SiC allows using epitaxial graphene nowadays for quantum metrology. While it is known that the interface between graphene and the SiC surface is crucial for graphene's transport properties, almost no information about the composition of the SiC substrate after the sublimation process is available. In this study we present high resolution c(s)-corrected scanning transmission electron microscopy (STEM) experiments on 6H-SiC(0001) samples after growth of graphene. A Si deficiency within the first three SiC bilayers was found by atomically resolved energy dispersive x-ray spectroscopy (EDX). The Si concentration within the first bilayer can be reduced up to 50%. In addition, as probed by electron energy loss spectroscopy, the hybridization state of C within the first five bilayers revealed a sp(2) contribution, which we refer to as the precipitation of small carbon clusters. Our analysis clearly shows that the electronic interface of epitaxial graphene on 6H-SiC(0001) is not atomically sharp.