Influence of Cu overlayers on the interaction of CO and CO2with ZnO(0001)-O

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Abstract
NEXAFS and FT-RAIRS have been used to investigate the adsorption of CO and CO2 on ZnO(000 text-decoration:overline1)-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(000 text-decoration:overline1)-O which are uncovered during the onset of 3D island growth.