Electronic states and local structures of Cu ions in electrodeposited thin films of Cu and Cu2O from X-ray absorption spectra

Abstract

X-ray absorption spectra near Cu K edges have been obtained for Cu and Cu2O thin films potentiostatically electrodeposited in an acetate bath. The electronic states of Cu ions and the local structures around these ions are studied using X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy, respectively. The inner strains in micro-size crystals of the electrodeposited Cu thin film are less than those of a commercial Cu foil. The partial electronic states of Cu ions near the Fermi level (EF) and the local structure around these ions show a systematic transformation from a Cu2O single phase (Phase I), to a Cu2O?Cu intermediate phase (Phase II) and a Cu single phase (Phase III) in thin films electrodeposited on titanium substrates for the deposition potential range of ?100 to ?900 mV. Phase II consists of independent Cu2O-like and Cu-like local structures, but not a Cu2O?Cu complex. Phase II is also characterized by a transition region from the semiconductor Cu2O to the metal Cu for the Cu electronic state having a p-like character near the Fermi level in the oxygen O-2p conduction band. (? 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)