NEXAFS study of CO adsorption on ZnO(000(1)over-bar1)-O and ZnO (000(1)over-bar)-O/Cu

C K-edge near edge X-ray absorption fine structure (NEXAFS) measurements ha ve been used to investigate CO adsorption at 130 K on ZnO(000 (1) over bar) -O and on the same surface after a 2D submonolayer Cu film has been deposit ed. CO adsorption on clean ZnO(000 (1) over bar)-O gives rise to two pi* re sonances in the NEXAFS spectra at 287.7 +/- 0.2 eV and 290.4 +/- 0.2 eV. Th ese are assigned to molecular CO, which is metastable under our experimenta l conditions, and CO32-. Only one intense pi* resonance, at 287.7 +/- 0.2 e V, is observed for CO adsorption on ZnO(000 (1) over bar)-O after submonola yer Cu deposition. This is also attributed to adsorbed molecular CO. The po larisation dependence of this resonance indicates that the CO molecular axi s is tilted by 17 +/- 10 degrees away from the surface normal. (C) 1999 Els evier Science B.V. All rights reserved.