Application of reflectance spectrophotometry to the study of copper (I) oxides (Cu ₂ O and Cu ₃ O ₂ ) on metallic substrate

The aim of this study is to characterize the compounds grown on copper during the oxidation at low temperature (T < 523 K) by optical methods: photoluminescence and UV‐Visible‐NIR diffuse reflectance spectroscopy. Two cuprous oxides Cu 2 O and Cu 3 O 2 have been studied. The absorption of Cu 2 O films in the range 450–630 nm is mainly due to non‐stoichiometry bands associated with copper and oxygen vacancies. Cu 3 O 2 is characterized by an optical band gap greater than that of Cu 2 O (respectively 2.25 and 1.95 eV) and by an intense luminescence emission at 760–780 nm. Cu 3 O 2 may be considered as a gross defect structure of Cu 2 O (a = 0.427 nm, a = 0.431 nm). The experimental approach of the oxidation mechanism reveals that at 423 K Cu 2 O is the primary product which later on is transformed into Cu 3 O 2 . Experimental and calculated optical absorption curves disclose the nucleation of CuO inside the cuprous oxides layer for oxidation in the range 473–523 K.