CROSS-SECTIONAL STRUCTURE OF TETRAHEDRAL AMORPHOUS-CARBON THIN-FILMS

A cross-sectional transmission electron microscope study of the low de nsity layers at the surface and at the substrate-him interface of tetr ahedral amorphous carbon (ta-C) films grown on (001) silicon substrate s is presented. Spatially resolved electron energy loss spectroscopy i s used to determine the bonding and composition of a tetrahedral amorp hous carbon film with nanometre spatial resolution. For a ta-C film gr own with a substrate bias of -300 V, an interfacial region approximate ly 5 nm aide is present in which the carbon is sp(2) bonded and is mix ed with silicon and oxygen from the substrate. An sp(2) bonded layer o bserved at the surface of the film is 1.3+/-0.3 nm thick and contains no detectable impurities. It is argued that the sp(2) bonded surface l ayer is intrinsic to the growth process, but that the sp(2) bonding in the interfacial layer at the substrate may be related to the presence of oxygen from the substrate.