A NEXAFS investigation of the formation and decomposition of CuO and Cu2O thin films on Cu(100)

We report the use of near-edge X-ray absorption fine structure (NEXAFS) to unambiguously characterize the oxidation state of copper in copper oxides. The method is based on the analysis of the oxygen K-edge and copper L-edge features of Cu2O and CuO powder materials. To further demonstrate its utili ty, NEXAFS was also used to follow spectroscopically the oxidation of a Cu( 100) single crystal surface by NO2, and the thermal decomposition of the re sulting oxides. In agreement with previous studies [J.A. Rodriguez, J. Hrbe k, J. Vac. Sci. Technol, 12 (1994) 2140], our NEXAFS results indicate that NO, dissociates on the metal surface, generating NO and atomic oxygen which subsequently reacts with the Cu(100) surface to produce Cu2O (300 K) or a mixture of Cu2O and CuO (250 K). Upon heating, the thermodynamically unstab le CuO transforms into Cu2O. (C) 1999 Elsevier Science B.V. All rights rese rved.