Silicon effect on the hardness of r.f. Sputtered B-C: Si amorphous films

B-C and B-C:Si films were deposited by r.f. magnetron sputtering from a hot-pressed B₄C polycrystalline target with Si pieces placed on the preferentially eroded zone. The effect of Si content, ranging from 2 to 6 at-%, on the B-C films was studied at a fixed substrate bias of -70 V. Preliminary depositions with different substrate bias showed that with -70 V the deposition of free carbon was avoided. All deposited films were X-ray diffraction (XRD) amorphous, and the result was confirmed by Fourier transform infrared spectroscopy (FTIR). Si-containing films were harder than Si-free ones, reaching 30 GPa for compositions up to 4.5 at.-% Si. After thermal annealing of the B-C:Si films up to 700 °C, an increase of the hardness was observed. The maximum hardness of 37 GPa was obtained for 2 at-% Si film annealed at 600 °C, which corresponds to an increase of -23% in relation to the as-deposited conditions. No vestiges of crystallinity were found either by XRD or FTIR analysis suggesting that the structure of the Si-containing films consisted of a local order arrangement of boron-rich icosahedral units