Positron annihilation spectroscopy of sputtered boron carbide films

Positron annihilation spectroscopy (PAS) was carried out on boron carbide films deposited by sputtering and the results correlated to the bombardment conditions during film growth. Films were deposited with substrate bias voltages in the range of 0 to −200 V with a working pressure of 5 mTorr of Ar. Films deposited with bias voltages from −100 to −200 V present the same type of defect and the defect concentration increased linearly with the bias voltage. This defect was ascribed to vacancies in agreement with Monte Carlo simulations of Ar+ bombardment of boron carbide. On the other hand, films deposited with 0 V bias presented a higher S parameter values, whose origin was tentatively attributed to a relatively more open nanosized columnar structure, as suggested by the structure zone model. Annealing up to 800 °C for 30 min did not change the defect content.