Theoretical prediction of impurity effects on the internally oxidized metal/oxide interface: the case study of S on Cu/Al2O3.

A detrimental sulfur effect on adhesion is known for iron- and nickel-oxide interfaces, but has never been reported on copper-oxide interfaces. Here we present a first-principles based study on the effects of temperature, interfacial stoichiometry, Al activity, and S segregation on the internally oxidized Cu/α-Al(2)O(3) interface. The calculated "interfacial phase diagram" for temperatures of interest suggests that the equilibrium interface structure is near the transition between Al-rich and stoichiometric phases. The Al-rich type interface is significantly stronger than the stoichiometric counterpart. The S effect on the Cu/α-Al(2)O(3) interface is obvious: S strongly segregates to both types of interface, degrades the adhesion (by ∼65%) and also reduces the size stability of alumina particles in Cu.