ELASTIC-MODULUS OF AMORPHOUS-CARBON FILMS

The elastic moduli directly reflect bonding strength and structure. Us ually these factors can be only slightly modified within a given mater ial, but in amorphous carbon films large variations of Young's modulus from less than 100 up to more than 500 GPa are found. This can be att ributed mainly to the varying fraction of sp3 and sp2 bonds. Even for hard amorphous carbon films of diamond-like nature the modulus achieve s only 30 to 50% of crystalline diamond. The Young's modulus is measur ed by a specially developed method. It is based on the determination o f the frequency dependent propagation velocity of ultrasonic surface w aves and its mathematical evaluation. The potential of this nondestruc tive method is demonstrated for amorphous carbon films down to a thick ness of 100 nm. It turns out to be a suitable means for characterizing and classifying such films.