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