Effects of steps and defects on O2 dissociation on clean and modified Cu(1 0 0)

Dissociative chemisorption of O2 on Cu(1 0 0), S/Cu(1 0 0) and Ag/Cu(1 0 0) surface alloy has been investigated by Auger electron spectroscopy (AES). A strong reduction in the initial O2 chemisorption probability (S0) from 0.05 to 7.4 × 10−3 is observed already at an Ag coverage of 0.02 ML. Further Ag deposition results only in a moderate decrease in S0. Similar inhibition of O2 dissociation is observed on S/Cu(1 0 0). It is concluded that at very low Ag coverages, the reduced reactivity of Ag/Cu(1 0 0) towards O2 dissociation is primarily due to the steric blocking of the surface defects and that any electronic effects are only secondary and present only at higher Ag coverages.