Adsorption of CO on the copper-precovered ZnO(0001) surface: A molecular-beam scattering study

Auger electron spectroscopy (AES), thermal-desorption spectroscopy (TDS), and, in particular, molecular-beam scattering techniques have been combined to address particle size effects in the adsorption of CO on Cu-on-ZnO(0001). AES and TDS lead to a Cu coverage, Theta(Cu), calibration. The TDS curves, as a function of Theta(Cu) and CO exposure, revealed three structures at 150, 220, and 260-280 K, in agreement with prior studies. However, a unique assignment of the TDS structures to a particular Cu face was not possible. An enhancement of the initial adsorption probability, S-0, with respect to the support indicates the effect of the Cu nanoparticles. Despite that the shape of S-0 versus impact energy curves was independent of Theta(Cu) and agreed with Cu single-crystal reference systems, distinct particle size effects were present with regard to the adsorption mechanism. It was possible to observe a crossover from Langmuir-type adsorption dynamics to more precursor-assisted adsorption dynamics with increasing Theta(Cu). Thus, a dynamic structure-activity relationship was evident, i.e., the energy-transfer mechanism depends on the Cu morphology.