Hardness and modulus properties in ion-beam-modified amorphous carbon: Temperature and dose rate dependences

Ion implantation into amorphous carbon has been initiated to investigate the possibility of superhard carbon-nitride formation. Studies of implantation-temperature effects by 100 keV N+ or 80 keV C+ ions at 50 mu A show a narrow temperature window at approximately -100 degrees C for the optimum surface hardness and elastic modulus (measured by nanoindentation), both values much higher than those for the unimplanted amorphous carbon. No distinguishable properties are found between nitrogen and self (carbon) implantations. At a dose rate of 5 mu A, however, the optimum hardness and modulus are found at a lower implantation temperature, with a broader temperature window. The enhanced strengths are well correlated with the asymmetric diffuse peak at around 1500 cm(-1) in Raman spectroscopy, and the increased ratio of sp(3)- over sp(2)-bonded carbon sites observed by electron energy loss spectroscopy.