Influence of Cu overlayers on the interaction of CO and CO2 with ZnO(0001 )-O

Abstract

NEXAFS and FT-RAIRS have been used to investigate the adsorption of CO and CO₂ on ZnO(0001)-O and its modification by copper overlayers. NEXAFS data indicate a CO₃^2– species with the molecular plane within 30° of the surface normal following CO and CO₂ adsorption on the clean surface at 130 K. Upon low-temperature deposition of a submonolayer Cu film, CO₃^2– species were no longer formed following CO adsorption, although molecular CO was evidenced with the molecular axis within 20° of the surface normal. A single ν(CO) band observed in FT-RAIRS indicates that the CO is adsorbed on 2D Cu(110)-like sites in an atop position. Preannealing the Cu film to 400 K led to a redistribution of Cu into 3D islands, as evidenced by FT-RAIRS. Exposure to CO of such a surface at 130 K resulted in both CO and CO₃^2– formation. This suggests that Cu initially nucleates at the active sites for CO₃^2– formation on ZnO(0001)-O which are uncovered during the onset of 3D island growth.