Copper passivation by metal doping

Abstract

A computational Density Functional Theory (DFT) study of metal-doped copper surfaces and their reactivity with atomic oxygen is reported. The surface segregation and passivation potential of several different dopant metals (Mg, V, Cr, Al and Zn) on Cu(1 1 0) surface was investigated. The dopant atoms were placed on different layers of the surface, and the interaction with oxygen was studied at a coverage of 0.25 ML. Without oxygen the Mg, Al and Zn will segregate to the surface but the segregation energies are not large. The presence of oxygen changed this situation dramatically, now in all cases the metals will segregate to the surface and the segregation energies are large except for zinc. Also the sub-surface dopant layers will increase the oxygens binding to the Cu(1 1 0) surface. This suggests that the oxygen will enrich the dopants to and near to the surface and in this way helps to form a passivating layer on the copper alloy. The role of the surface orientation and the oxygen coverage was investigated with Al-doped Cu(1 1 0), Cu(1 0 0) and Cu(1 1 1) surfaces. The results shows that Al should segregate on the surface layer, and the enrichment is more pronounced with the more dense surfaces (1 1 1) and (1 0 0). Also the oxygen coverage was tested with Al-doped Cu(1 1 0), Cu(1 0 0) and Cu(1 1 1) surfaces. The coverage varied from 0 to 1.0 ML. The calculated segregation energies are negative in all coverages, and they increase rapidly with the oxygen coverage. This indicates that aluminium has a strong tendency to segregate to the surface, making Al a good passivation element for copper surfaces.