Characterization of the initial stages of copper oxidation by optical absorption and photoluminescence

Caractérisation des premiers stades de l'oxydation du cuivre par absorption optique et par photoluminescence.

Abstract

Optical methods are easy to use and give useful informations on oxidation products. In the case of copper oxides, layers from several nanometers up to several micrometers thick can be studied. The following oxides : CuxO precursor of Cu₂O, Cu₂O, Cu₃O₂ and CuO are characterized by UV-Vis-NIR diffuse reflectance spectroscopy. The defects in cuprous oxides may be identified by photoluminescence spectra. The oxide formed at 423 K for long oxidation times is Cu₃O₂. In the 473-573 K temperature range, the outer layer is a mixture of CuO and copper (I) oxides and periodic changes in the composition of the layer are observed in the early stages of oxidation. The experimental data observed at 573 K indicate that the oxidation involves a fast process of Cu to Cu₃O₂ (2 Cu + 1/2 O₂ -> Cu₂O and 3 Cu₂O + 1/2 O₂ -> 2 Cu₃O₂) and a slow process for the formation of CuO. For copper oxidation at T > 673 K, the corrosion layer is a multiphase and multilayer structure : CuO/Cu₃O₂/Cu₂O/Cu.