MICROSTRUCTURE OF AMORPHOUS C-H AND METAL-CONTAINING C-H FILMS DEPOSITED ON STEEL SUBSTRATES

Cross-sectional transmission electron microscopy (XTEM), including high-resolution microscopy (HREM), was employed to characterize the interface between different amorphous hydrogenated carbon (a-C:H) films and steel substrates. Additional analyses using Auger electron spectroscopy (AES) and X-ray diffraction (XRD) were also performed. Films were deposited both by high-energy (50 keV) nitrogen ion-beam decomposition of large hydrocarbon molecules and by magnetron plasma decomposition of C2H2 in mixed Ar-C2H2 discharges. The latter method was also used to deposit Mo- or W-containing a-C:H films (Me-C:H films) onto steel substrates with interlayers of the pure metals between the substrate and Me-C:H film. The films were found to be truly amorphous except for the cases of the metal-containing films, where 1-2 nm crystalline clusters were present in an a-C:H matrix. In the case of Mo the clusters were identified from HREM micrographs to have a bcc-like structure, characteristic of metallic Mo. The metal interlayers had a columnar microstructure with column widths of approximately 30 nm. The interfaces between the Mo and W interlayers and the a-C:H films 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 layer (< 10 nm) was observed which was predominantly amorphous but contained a small fraction of crystalline grains. AES showed an increase of 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 of the substrate and metal interlayer phase were continuous across a sharp interface.