Elastic properties of hydrogen-free amorphous carbon thin films and their relation with carbon-carbon bonding

The hardness and elastic modulus of thin, free of hydrogen, amorphous carbo n (a-C) films, deposited with sputtering, were measured using the nanoinden tation. conventional and continuous stiffness measurements (CSM). depth-sen sing techniques. It is shown that the CSM technique is quite efficient in c haracterizing very thin (similar to 30 nn) a-C films. The sp(2) and sp(3) c ontent and thickness of a-C films were determined with spectroscopic ellips ometry. Films deposited with ion bombardment during growth exhibit high har dness and elastic modulus due to the formation of high fraction of sp(3) si tes supporting an interrelation between elastic properties and C-C bonding. We have also found that a-C films deposited with alternating layers, rich in sp(2)/rich in sp(3) content, exhibit even higher hardness and elastic mo dulus and above those so far reported for sputter-produced a-C films. The e nhancement of the elastic properties is possibly due to either the formatio n of compositional smooth interfaces between the two type of layers or due to the curved and cross-linked graphite planes in the sp(3)/sp(2) rich inte rfacial region. (C) 1999 Elsevier Science S.A. All rights reserved.