INFLUENCE OF CU OVERLAYERS ON THE INTERACTION OF CO AND CO2 WITH ZNO(000(1)OVER-BAR)-O

NEXAFS and FT-RAIRS have been used to investigate the adsorption of CO and CO2 on ZnO(<000(1)over bar>)-O and its modification by copper ove rlayers. NEXAFS data indicate a CO32- species with the molecular plane within 30 degrees of the surface normal following CO and CO2 adsorpti on on the clean surface at 130 K. Upon low-temperature deposition of a submonolayer Cu film, CO32- species were no longer formed following C O adsorption, although molecular CO was evidenced with the molecular a xis within 20 degrees of the surface normal. A single v(CO) band obser ved in FT-RAIRS indicates that the CO is adsorbed on 2D Cu(110)-like s ites in an atop position. Preannealing the Cu him to 400 K led to a re distribution 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 CO32- format ion. This suggests that Cu initially nucleates at the active sites for CO32- formation on ZnO(<000(1)over bar>)-O which are uncovered during the onset of 3D island growth.