Preparation and characterization of superhard boron-suboxide films

Boron-suboxide films with hardness reaching 44 GPa, the highest record ever achieved, were synthesized. The films with such high hardness had an oxygen/boron atomic concentration ratio of 0.05 and a carbon concentration of about 20 at. %. They were deposited on silicon at 750 °C by simple sputtering. In the range of oxygen/boron ratio varying from 0.06 to 0.3, the film hardness and elastic modulus decreased monotonically. Unlike other hard film formation, argon ion bombardment of the film during film growth reduced the film hardness.