Formation and characterization of infrared absorbing copper oxide surfaces

Copper oxide formation has been investigated to combine the advantages of producing different size and shapes of coatings that possess good light absorbing properties. An aqueous blackening solution was investigated and optimum composition was found as 2.5 M NaOH and 0.225 M NaClO to form velvet copper oxide films. A two-step oxidation mechanism was proposed for the blackening process by carefully examining the experimental results. Formation of Cu₂O was observed until the entire copper surface was covered at first. In the second step, Cu₂O surface was further oxidized to CuO until the whole Cu₂O surface was covered by CuO. Therefore, blackened copper surfaces consisted of Cu₂O/CuO duplex oxides. Characterization of the coatings were performed in terms of microstructure, phase analysis, chemical state, infrared specular and total reflectivity by SEM, XRD, XPS, FTIR and UV-vis spectrophotometry, respectively.