Influence of carbon content on the crystallographic structure of boron carbide films

Boron carbide thin films were synthesised by laser-assisted chemical vapour deposition (LCVD), using a CO2 laser beam and boron trichloride and methane as precursors. Boron and carbon contents were measured by electron probe microanalysis (EPMA). Microstructural analysis was carried out by Raman microspectroscopy and glancing-incidence X-ray diffraction (GIXRD) was used to study the crystallographic structure and to determine the lattice parameters of the polycrystalline films. The rhombohedral–hexagonal boron carbide crystal lattice constants were plotted as a function of the carbon content, and the non-linear behaviour observed was interpreted on the basis of the complex structure of boron carbide.