From the depth profiles in Fig. ) and b), we note an accumulation of oxygen at the film substrate interface in both hydrogen and argon ambient. The oxygen content decreases to a value around 1 at.% in the bulk of the film. We observe that this variation in oxygen concentration from film-substrate interface to film surface, irrespective of ambient gas, is due to the presence native oxide layer on the top of the Si substrate. The chemical bonding structure in the films as determined by XPS (Fig. ) shows that the B 1s core level spectra can be fitted by three chemical environments with peaks centered at 188.2 eV, 189 eV and 191 eV. The dominant peaks at 188.2 eV and 189 eV are attributed to B-B and B-C chemical bonds, respectively. The small component peak at 191 eV indicates B-O formation. We attribute this to oxidation of elemental boron present in the film due to post deposition air exposure. The C 1s spectra are fitted by three distinct chemical states with energy peaks at 282.9 eV, 284.2 eV and a low intensity peak at 246.2 eV. The peak energy position 284.2 eV is identified as signals from C─C bonds present in the film. The peak at 282.9 eV is attributed to of C-B chemical bond. The small component peak at 246. The film density was estimated from the XRR plots fitted for BxC films deposited at varying temperatures from 425 to 550 °C. The density values were found to have dependency with deposition temperature, and this correlation is plotted in Fig. together with the reflectivity curves and the fitting curves. At 425 °C deposition temperature, the film had a density of 1.90 g/cm 3 with a critical angle for total external reflection of ~0.19° (Ө). The film deposited at 550 °C had a density of 2.28 g/cm 3 with a critical angle of ~0.21°, which can be compared with the reported bulk density of 2.52 g/cm 3 for B4C .