Initial and later stages of anodic oxide formation on Cu, chemical aspects, structure and electronic properties

The formation of OH adsorption layers and the initial and later stages of t he growth of anodic oxide have been studied on Cu(111) single crystal surfa ces with STM. In 0.1 M NaOH Cu forms OH- adsorption layers for E > - 0.57 V (SHE) whereas oxide formation occurs at E > - 0.22 V. The adsorption of OH - and oxide formation can be followed by in situ electrochemical STM. At su fficiently high negative potentials even time resolved investigations becom e possible. OH adsorption goes along with a surface reconstruction. Oxide f ormation starts with small non-crystalline grains and with oxide crystals i n a later stage. In borax buffer pH 9.2 no stable image is obtained during the growth of the Cu2O films with d > 1 nm whereas the images of the duplex layer formed at higher potentials are stable again. These details are disc ussed on the basis of previous results on the chemical composition of the p assive layer in alkaline solutions and its semiconducting properties obtain ed from XPS, UPS, and electrochemical and photoelectrochemical investigatio ns. (C) 2001 Elsevier Science Ltd. All rights reserved.