We instead consider the possibility that our deposition process operates in a window where the substrate, especially the C-face, may act as a carbon source but at a rate that prevents the formation of graphene. The second source of carbon in our process is evidently TEB, or rather, its main decomposition by-product, C2H4 ; the decomposition of which is kinetically slower but can ultimately lead to the formation of acetylene and in turn of pyrolytic graphite, if the temperature is high enough and/or the residence time long enough . From our results, we note that when the Si-terminated surface is used with a relatively short residence time, the texture of the films varied strongly with temperature, while for longer residence time the [0003] orientation prevails, until graphite forms. We suggest that this can be explained by the fact that a delicate balance of carbon concentration at the 4H-SiC(0001) surface may be needed to promote the growth of boron carbide along the c-axis. At lower temperatures (1200 °C and below), the Si-face is not an efficient carbon source on its own and the decomposition rate of the C2H4 byproducts is slow, leading to growth along the [0003] orientation only for the longest residence times. Around 1300 °C the carbon concentration is adequate to promote nucleation along the c-axis, although the films remain polycrystalline. Above 1300 °C, graphite forms and consumes the carbon provided by the C2H4 byproducts and again prevents the films from growing along the c-axis. In contrast, the C-face would be a more efficient C-source, making the growth less depending on the carbon coming from the gas phase and less sensitive to the formation of graphite.