Characterization of RF-sputtered iron oxide films for modeling passive films

Iron oxide films were r.f.-sputtered on metallic, ceramic and polymeric substrates in order to study the structure, composition and the photo-electrochemical properties of the coatings. The formed iron oxide phase was Found to depend on the substrate biasing during deposition, The main phases obtained were alpha-Fe2O3 and Fe3O4. The films had 3 tendency to form a columnar structure, which was more preferred on metallic substrates. The alpha-Fe2O3 target was found to be reduced during the sputtering, and a mixed oxide of alpha-Fe2O3 and Fe3O4 was formed. The orientation of the deposited films was found to be dependent on the formed phase, the substrate voltage and the target composition. The deposition rate was dependent on the formed phase, biasing and substrate material, as well as on the level of the reduction of the target. The films were nanocrystalline, having crystal sizes of 10 nm or less. The Fe2+ content was found to have an effect on the measured photocurrents. Roughness of the semiconductor surface was noticed to have a strong influence on the AC impedance of the sputtered oxide layers. X-ray absorption near edge spectroscopy (XANES) measurements revealed further information on the oxidation state of the sputter-deposited iron oxide films. (C) 1998 Elsevier Science S.A.