Chromium interlayers as a tool for enhancing diamond adhesion on copper

Abstract

Abstract Diamond films on copper suffer from poor adhesion, mainly due to the lack of affinity between carbon and copper. In this study a chromium (Cr) interlayer has been employed to improve the adhesion between the diamond films and the copper substrates. The Cr interlayer, a carbide-forming material, plays the role of an adhesive between the diamond film and the copper substrate. A hot filament chemical vapour deposition (HFCVD) system, modified to enable the substrate to be negatively biased has been used to deposit diamond. It was observed that diamond nucleation together with the deposition rate increased with bias time. A bias time of 5 min was sufficient to increase diamond nucleation and enhance the growth rate. The diamond films deposited exhibited predominantly 〈111〉 orientation, as evident from the SEM micrographs. Diamond films grown on the Cr-coated Cu substrates gave reasonable adhesion values. Pull-off tests showed that the adhesion was better than the strength of the adhesive employed, ∼14 MPa. Scratch tests revealed a critical load of ∼7 N with unbiased samples, while the critical load increased significantly to ∼38 N for samples pre-treated at –250 V for 15 min. Furthermore, it was found from Raman analysis that films with better adhesion exhibited greater Raman shift of the 1332 cm −1 diamond peak. The overall results suggest that Cr is an effective interlayer for producing adherent diamond coatings onto Cu substrates.