Growth Mechanism and Cross-Sectional Structure of Tetrahedral Amorphous Carbon Thin Films

Abstract

Spatially resolved electron energy loss spectroscopy is used to characterize the cross-sectional structure of highly tetrahedral amorphous carbon films, particularly concentrating on the ${\mathrm{sp}}^{2}$ bonded surface layer. The surface layer is shown to be due to subsurface conversion from ${\mathrm{sp}}^{2}$ to ${\mathrm{sp}}^{3}$ 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 $0.4\ifmmode\pm\else\textpm\fi{}0.2\mathrm{nm}$ for 35 eV ions to $1.3\ifmmode\pm\else\textpm\fi{}0.3\mathrm{nm}$ for 320 eV ions. The influence of growth temperature is investigated, and it is found that the temperature above which ${\mathrm{sp}}^{3}$ bonding is not stable is greatly reduced in the region affected by ion bombardment.