Pull‐test adhesion measurements of diamondlike carbon films on silicon carbide, silicon nitride, aluminum oxide, and zirconium oxide

Hydrogenated amorphous carbon or diamondlike carbon (DLC) films were formed by 400 eV methane (CH₄) ion bombardment of various smooth and rough ceramics, as well as ceramics coated with a layer of Si or Ti. Adhesion was measured by a bonded‐pin method. Excellent adhesion was measured for smooth SiC and Si₃N₄, but adhesion of DLC to smooth Al₂O₃ and ZrO₂ was negligible. The use of a Si bonding interlayer produced good adhesion to all the substrates, but a Ti layer was ineffective due to poor bonding between the DLC film and Ti. Bulk thermodynamic calculations are not directly applicable to bonding at the interface because the interface is two dimensional and the compositions of interfacial phases are generally not known. If the standard enthalpy ΔH° for the reaction between CH₄ and the substrate material is calculated under the assumption that a carbide phase is produced, a relationship is seen between the reaction enthalpy and the relative adhesion. Large positive enthalpies are associated with poor adhesion; negative or small positive enthalpies are associated with good adhesion. This relation between enthalpy and adhesion was also observed for DLC deposited on Si. The lack of adhesion to the Ti was attributed to inadvertent formation of a surface oxide layer that rendered the enthalpy for the reaction with CH₄positive.