Delafossite CuFeO₂ thin films electrochemically grown from a DMSO based solution

This study shows the results obtained in the direct electrodeposition of CuFeO₂ thin films from a DMSO based solution. First, a detailed electrochemical study was carried out in order to determinate the best condition for the CuFeO₂ electrodeposition. The films were obtained potentiostatically from a 0.01 M CuCl₂ + 0.005 M Fe(ClO₄)₃ + 0.1 M LiClO₄ solution in the presence of molecular oxygen at 50 °C onto FTO/glass substrates. In all cases, the time of electrodeposition was 1000 s. The grown films presented a yellow-reddish color and exhibit an homogeneous aspect. Analyses of composition carried out through EDS, shown that a stoichiometric composition (atomic relation Cu:Fe = 1:1) is obtained at a potential of -0.6 V. However, as-grown films analyzed through XRD experiences did not evidence the presence of CuFeO₂ compound presumably because it is amorphous. An annealing treatment at 650° C for 30 minutes in an argon atmosphere was necessary to transform the solid phase of the as grown films in crystalline CuFeO₂. Furthermore, the presence of CuFeO₂ has been confirmed through XPS analyses. UV-vis analyzes shown a ladder-like appearance due to the presence of several absorption edges from the IR to the UV spectrum region. The most clearly determined were a direct-like edge at the IR: E_g(IR) = 1.64 eV. However, several absorption edges in the visible (E_g^dir(vis) = 2.35 eV, and E_g^ind(vis) = 2.03 eV) and UV beginning (E_g^ind(UV) = 3.37 eV) spectrum region also were observed.