Characterization of copper-manganese-oxide thin films deposited by dip-coating

Thin films of copper-manganese oxide were prepared by dip-coating method and annealed between 400 and 500 degrees C for periods of time from 15 to 90 min. The influence of both annealing time and temperature on film composition and optical properties was studied. X-ray photoelectron spectroscopy (XPS) measurements indicated that the initially formed mixture of copper an manganese oxides leads to Cu1.5Mn1.5O4 through a solid state red-ox reaction. This reaction takes place at temperatures higher than 450 degrees C and the full conversion of single oxides into CU1.5Mn1.5O4 needs at least 60 min to proceed. In relation to the optical properties we found that low solar absorptance (alpha(s)similar to 0.6) can be associated with the mixture of single oxides whereas the formation Of Cu1.5Mn1.5O4 dramatically increases solar absorptance values (alpha(s)similar to 0.9). The presence of Mn3+ and Mn4+ in octahedral sites and Cu+ and Cu2+ in tetrahedral sites is also evidenced by XPS and can explain the high conductivity of films where Cu1.5Mn1.5O4 is present. (C) 2008 Elsevier B.V. All rights reserved.