4 and Fig. ). It should be noted that the epitaxial r-B4C film on the C-face and the polycrystalline film on the Si-face (Fig. ) were both grown in the same CVD experiment. Higher carbon content is observed in the first few nanometers of the r-B4C film on the C-face compared to the Si-face (Fig. ). Given that r-B4C grew epitaxially on the C-face, we could reason that this initial carbon in the film may be important for the initial stages of epitaxial growth of r-B4C films on 4H-SiC. The B atoms in B4C form caged structures which leads to the characteristic network of boron icosahedra seen in boron carbide. The suggested role of carbon is to stabilize this network by supplying electrons to the boron icosahedron. However, these considerations rely heavily on the experimental results from the EELS analysis alone and the supporting reasoning is highly speculative. This could also be a consequence of epitaxial growth and not necessarily the reason for it.