S. Logothetidis et C. Charitidis, Elastic properties of hydrogen-free amorphous carbon thin films and their relation with carbon-carbon bonding, THIN SOL FI, 353(1-2), 1999, pp. 208-213
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.