Adsorption probability of CO on a metal oxide: The case of oxygen-terminated ZnO and the influence of defects

We present measurements of the coverage dependence of both the adsorption probability and He-atom reflectivity for CO on oxygen terminated ZnO(0001) surfaces. Two samples with significantly different defect density, as characterized by He-atom scattering, have been investigated. The comparison of adsorption probability and He reflectivity curves strongly suggest that initially only defect sites are populated by the CO molecules. The shape of the coverage-dependent adsorption probability curves indicates the presence of precursor mediated adsorption.