Adhesion and adhesive transfer at aluminum/diamond interfaces: A first-principles study

Using a first-principles methodology, we investigated the effect of diamond surface termination on the work of separation (Wₛₑₚ), interface geometry, bond character, and adhesive transfer of three Al/diamond interfaces, viz., Al(111)/C(111)-1×1, Al(111)/C(111)-2×1 and Al(111)/C(111)-1×1:H. Bond character was explored with the electron localization function. Adhesive transfer was investigated by subjecting each interface to a series of tensile strain increments up to fracture. This also allowed us to generate constitutive laws for decohesion and predict the interfacial strength. The highest adhesion occurs in Al(111)/C(111)-1×1 for which Wₛₑₚ=4.08J/m². Adhesion is due to strong covalent Al-C bonds, and two Al layers transfer to the diamond. Mixed covalent/metallic bonds form along Al(111)/C(111)-2×1, for which Wₛₑₚ=0.33J/m², and fracture occurs without adhesive transfer. Bond breaking in the clean interfaces is accompanied by a jump-to-separation process. We also find that Al(111)/C(111)-1×1 is energetically favored over Al(111)/C(111)-2×1 even though the latter contains reconstructed diamond. This suggests that the reconstruction of C(111)-2×1 is broken upon exposure to Al. For Al(111)/C(111)-1×1:H, we computed Wₛₑₚ=0.02J/m²; no bonds form between Al and H and fracture occurs without adhesive transfer. Qualitative comparison of our results with existing experiments is also presented.