ELASTIC-MODULUS AS A MEASURE OF DIAMOND LIKENESS AND HARDNESS OF AMORPHOUS-CARBON FILMS

The elastic modulus directly reflects the bonding strength and structu re of a solid state. Usually this factor can only be modified slightly for a given material, but in amorphous carbon films large variations in Young's modulus (from less than 100 GPa up to more than 500 GPa) ar e found. This can be attributed mainly to the varying fraction of sp(3 ) and sp(2) bonds. Even for hard amorphous carbon films of diamond-lik e nature, the modulus achieves only 30%-50% of the value of crystallin e diamond. Young's modulus was measured by a method based on the deter mination of the frequency-dependent propagation velocity of ultrasonic surface waves and its mathematical evaluation. The potential of this non-destructive method has been demonstrated for amorphous carbon film s down to a thickness of 100 mm. In addition to reference films deposi ted by various methods, films prepared by pulsed are processes were in vestigated systematically. The influence of the technological key para meters (ion flux, substrate temperature and hydrogen content) has been stressed. The changes in elastic modulus reflect directly the diamond likeness of the carbon-carbon network. Hence, Young's modulus represe nts a suitable parameter for the quantitative characterization and cla ssification of amorphous carbon materials. Apart from certain contribu tions by compressive internal stresses, the hardness can be estimated to be about one-tenth of the elastic modulus.