DECOMPOSITION OF NO2 ON METAL-SURFACES - OXIDATION OF AG, ZN, AND CU FILMS

The dissociation probability Of O2 on Cu(111), Ag(111), and Zn(001) surfaces is quite low (< 10(-2)). The oxidation process using molecular oxygen is not practical for work under ultrahigh vacuum conditions. We have found that NO2 is a very good oxygen source for the oxidation of Ag, Zn, and Cu surfaces. At elevated temperatures (300-500 K), the dissociation probability of NO2 on thick Ag, Zn, and Cu films supported on Ru(001) is close to one. The decomposition of NO2 produces a large amount of adsorbed oxygen and gaseous NO and N2. The thermal stability and electronic properties of the O/Ag, ZnO(x), and CuO(x) films were examined using temperature desorption spectroscopy, x-ray photoelectron spectroscopy (XPS), and x-ray Auger electron spectroscopy. Large amounts of oxygen can be adsorbed and dissolved in Ag films without oxidation of die noble metal. The zinc oxide films displayed the typical O 1s XPS and Zn L3M4,5M4,5 Auger spectra of polycrystalline ZnO. In addition, the high-resolution electron energy-loss spectroscopy spectra of these films exhibited the characteristic phonon losses of bulk ZnO. In the case of Cu films the NO2-oxidation leads to the formation of a mixture of CuO and CU2O. The CuO species is relatively unstable and can be reduced to CU2O by annealing at 700 K (2 CuO-->Cu2O+1/2O2) or by direct reaction with metallic Cu at 300 K (CuO+Cu-->Cu2O).