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 carbon (a-C) films, deposited with sputtering, were measured using the nanoindentation. conventional and continuous stiffness measurements (CSM). depth-sensing techniques. It is shown that the CSM technique is quite efficient in characterizing very thin (similar to 30 nn) a-C films. The sp(2) and sp(3) content and thickness of a-C films were determined with spectroscopic ellipsometry. Films deposited with ion bombardment during growth exhibit high hardness and elastic modulus due to the formation of high fraction of sp(3) sites 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 modulus and above those so far reported for sputter-produced a-C films. The enhancement of the elastic properties is possibly due to either the formation 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 interfacial region. (C) 1999 Elsevier Science S.A. All rights reserved.