Cu2O(1Â 1Â 0) formation on Co3O4(1Â 1Â 0) induced by copper impurity segregation

The impurities: K, Ca, Na, and Cu segregated to the surface after prolonged heating to 630 K. K, Ca and Na could easily be removed by routine cleaning procedures and did not affect the Co3O4(1 1 0) structure or stoichiometry detectably in the submonolayer levels at which they were observed. However, the copper impurity resulted in the formation of a Cu2O(1 1 0) overlayer, with the accompanying reduction of the spinel surface to a rocksalt metal monoxide-like surface. The copper oxide formed a distorted hexagonal overlayer incommensurate with that of the Co3O4(1 1 0) stoichiometric surface and with periodic spacings of 3.86 Å ± 0.2 Å in the 〈0 0 1〉 and 4.10 Å ± 0.2 Å in the 〈1¯10〉 directions in agreement with Cu2O(1 1 0) bulk termination. The Co3O4(1 1 0) substrate could not be fully re-oxidized until all detectable copper had been removed from the surface.