Nanoscratch testing of C60 thin films irradiated with N ions

Nanoscratch tests were performed in 170 nm thick C60 films using a depth sensing nanoindenter system with a lateral force measuring attachment. The films were irradiated with N+ ions at 170 keV and fluences ranging from 5x1011 to 5x1015 N/cm2. The scratches were 400 μm long and the used loads varied from 100 to 2500 μN. The measured friction coefficient changes from 0.23 for the C60 pristine film to 0.09 for the irradiated film with the highest fluence. The decrease in the friction coefficient with fluence is correlated with ion irradiation damage, total transferred energy density by the ions to the film and with film hardness