Characterization of interfaces between hydrogenated amorphous carbon films and steel substrates using high resolution cross-sectional transmission electron microscopy

Cross-sectional transmission electron microscopy, including high resolution microscopy, was employed to characterize the interfaces between hydrogenated amorphous carbon (a-C:H) films and steel substrates. Films were deposited both by ion beam decomposition of large hydrocarbon molecules and by magnetron plasma decomposition of C2H2. The latter method was also used to deposit Mo- and W-containing a-C:H films onto steel substrates with interlayers of the pure metals between the steel substrate and the a-C:H films. The films were found to be amorphous except for the metal-containing films where 1–4 nm crystalline clusters were present in an a-C:H matrix. The metal interlayers had a columnar microstructure with column widths of ∼30 nm. The interfaces between the a-C:H films and the Mo or W interlayers were found to extend over 20–40 nm with a gradual crystalline-to-amorphous transition. In most of the a-C:H film-substrate interface regions a thin (less than 10 nm) layer was observed which was predominantly amorphous, but contained a small fraction of crystalline grains. Additional analyses carried out using Auger electron spectroscopy showed an increase in both O and N close to the interface. However, for the cases with Mo and W interlayers, the substrate surface contaminants were less localized and on some parts of the substrate surface the lattice fringes were continuous across the atomically sharp interface.