  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 observed behaviour is interpreted on the basis of the complex
structure of boron carbide.
  Keywords: Boron carbide; Laser CVD; crystallographic structure; micro-Raman
spectroscopy.
