We also observe an increase in the oxygen signal starting from film nucleation from the EDX depth profiles of the r-B4C that grew epitaxially on the C-face. However, this difference could be a consequence of the epitaxial film's microstructure and the presence of voids (Fig. ). ERDA depth profiles for these films in the previous study showed 0.3% and 0.1 at% of O for the film grown on the C-face and the Si-face respectively. The difference is marginal from the ERDA analysis where the analyzed film is intact during measurements as opposed to the TEM sample preparation process done before the EDX analysis, as required. It is hard to differentiate between the oxygen incorporation during and after deposition, making this result less reliable.