Growth mechanism and cross-sectional structure of tetrahedral amorphous carbon thin films

Spatially resolved electron energy loss spectroscopy is used to characterize the cross-sectional structure of highly tetrahedral amorphous carbon films, particularly concentrating on the sp(2) bonded surface layer. The surface layer is shown to be due to subsurface conversion from sp(2) to sp(3) bonding at the depth of carbon ion implantation during film growth. The thickness of the surface layer is used as a measure of the ion penetration depth, varying from 0.4 +/- 0.2 nm for 35 eV ions to 1.3 +/- 0.3 nm for 320 eV ions. The influence of growth temperature is investigated, and it is found that the temperature above which sp(3) bonding is not stable is greatly reduced in the region affected by ion bombardment.