NARROW TEMPERATURE WINDOW FOR OPTIMUM ELASTIC-MODULUS IN ION-BEAM-MODIFIED AMORPHOUS-CARBON

We have investigated the possibility of superhard C3N4 formation by io n-beam implantation into amorphous carbon. The effect of the implantat ion temperature was examined using 100-keV N+ or 80-keV C+ ions. The a pparent elastic modulus data, measured by nanoindentation with load-di splacement, shows an optimum value of 91.0+/-0.9 GPa at approximately -100 degrees C. This is much higher than that for unimplanted amorphou s carbon, 35.5/-0.3 GPa. Self (carbon) implantation also produces simi lar modulus enhancements within a narrow temperature window. The maxim um elasticity correlates well with an asymmetric diffuse peak around 1 ,500 cm(-1) in the Raman spectra. A lower dose rate is found to furthe r strengthen the elastic modulus.