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

Abstract

Using a first-principles methodology, we investigated the effect of diamond surface termination on the work of separation ${(W}_{\mathrm{sep}}),$ interface geometry, bond character, and adhesive transfer of three Al/diamond interfaces, viz., $\mathrm{Al}\mathrm{}\left(111\right)/\mathrm{C}\mathrm{}\left(111\right)-1\mathrm{}\times 1,$ $\mathrm{Al}\mathrm{}\left(111\right)/\mathrm{C}\mathrm{}\left(111\right)-2\mathrm{}\times 1$ and $\mathrm{Al}\mathrm{}\left(111\right)/\mathrm{C}\mathrm{}\left(111\right)-1\mathrm{}\times 1:\mathrm{H}.$ 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 $\mathrm{Al}\mathrm{}\left(111\right)/\mathrm{C}\mathrm{}\left(111\right)-1\mathrm{}\times 1$ for which $W_{\mathrm{sep}}=4.08\mathrm{}{\mathrm{J}/\mathrm{m}}^2.$ Adhesion is due to strong covalent Al-C bonds, and two Al layers transfer to the diamond. Mixed covalent/metallic bonds form along $\mathrm{Al}\mathrm{}\left(111\right)/\mathrm{C}\mathrm{}\left(111\right)-2\mathrm{}\times 1,$ for which $W_{\mathrm{sep}}=0.33\mathrm{}{\mathrm{J}/\mathrm{m}}^2,$ and fracture occurs without adhesive transfer. Bond breaking in the clean interfaces is accompanied by a jump-to-separation process. We also find that $\mathrm{Al}\mathrm{}\left(111\right)/\mathrm{C}\mathrm{}\left(111\right)-1\mathrm{}\times 1$ is energetically favored over $\mathrm{Al}\mathrm{}\left(111\right)/\mathrm{C}\mathrm{}\left(111\right)-2\mathrm{}\times 1$ even though the latter contains reconstructed diamond. This suggests that the reconstruction of $\mathrm{C}\mathrm{}\left(111\right)-2\mathrm{}\times 1$ is broken upon exposure to Al. For $\mathrm{Al}\mathrm{}\left(111\right)/\mathrm{C}\mathrm{}\left(111\right)-1\mathrm{}\times 1:\mathrm{H},$ we computed $W_{\mathrm{sep}}=0.02\mathrm{}{\mathrm{J}/\mathrm{m}}^2;$ no bonds form between Al and H and fracture occurs without adhesive transfer. Qualitative comparison of our results with existing experiments is also presented.