Preparation and characterization of ferric oxyhydroxide and ferric oxide thin films by direct-hydrolysis deposition

We explore a novel wet-chemical process to form ferric oxyhydroxide and oxide films, direct-hydrolysis deposition, in which the substrate is immersed directly into a treatment solution to form films. The preferential film is obtained at a concentration of 20 mmol dm−3 Fe(NO3)3 solution and a reaction temperature of 60 °C. The film can be thickened by re-immersing it into a fresh treatment solution of the same concentration under the same condition, which results in the film thickness in the range of several hundred nm to several μm. Film characterization by Raman, SEM and XRD shows that the initial film is formed as γ-FeOOH. Heating the film in air at 400 °C converts it to α-Fe2O3. No other ions are introduced into the film.