First-principles study on the tensile strength and fracture of the Al-terminated stoichiometric α-Al2O3(0001)/Cu(111) interface

The first-principles tensile tests have been applied to the Al-terminated stoichiometric alpha-Al2O3(0001)/Cu(111) interface by using the ab initio pseudo-potential method based on the density-functional theory. Firstly, the Cu/Al and Cu/Cu interlayers have been examined by the rigid-type tensile test. The interlayer potential curves derived from the first-principles calculations are well fitted by the universal binding-energy relation (UBER) curves. The Cu-Al adhesion is weaker than the back Cu-Cu adhesion. Secondly, the relaxed-type tensile test has revealed the tensile strength and features of interfacial fracture. The ideal tensile strength is about 10 GPa, and the local Young's modulus is about 40 GPa, which means that the Cu/Al interface is quite weak and soft compared with the bulk regions and the O-terminated interface. The failure is initiated from the charge depletion region near the interfacial O atoms when the interlayer stretching exceeds about 30%, and the behaviour of electrons and ions indicates no strong Cu-O bond compared with substantial Cu-Al interactions. The present ab initio data are useful for the construction of effective interatomic potentials at the interface.