Synthesis of r-Fe₂0₃ Thin Films from Vacuum-Evaporated front

Abstract

Continuousγ-Fe₂O₃ thin films have been synthesized through an oxidation, a reduction and a mild oxidation processes. Iron thin films of 1100 A thick, starting material, were prepared. by evaporating iron on sapphire substrates and oxidized at 400°C in oxygen gas. The reduction was carried out at 320-400°C in argon gas, which was saturated with methanol at room temperature, and the mild oxidation in air at the temperature of 210-300°C. After the oxidation and the reduction processes, pure a-Fe₂O₃ and Fe₃O₄, were formed on the substrates, respectively. By adjusting the condition of the mild oxidation process, intermediary films with composition of Fe₃O₄ and Fe₂O₃ were obtained. The coercivities of the Fe₃O₄ and rFe₂O₃ films were 250 Oe and that of certain intermediary films were above 1000 Oe. The intermediary films were stable at room temperature and the gradual coercivity change was not detected, although the variation of it was reported for the fine particles of the same intermediate state. The thickness of the formed T-Fe₂O₃ films was 2900Å.. Irregular patterns of unevenness having a mean width of 1000Å and a mean depth of 450Å were observed on the surface of the films. The surfaces of the prepared films could be improved by removing the irregular surface layers. The mean crystal sizes were 280A for the evaporated iron films, 380Å for ce-Fe₂O₃, 340Å for Fe₃O₄, and 270Å for T-Fe₂O₃ films. The thickness of the iron films was 1100Å and was increased to 2900Å during the oxidation process. No detectable thickness change was observed during the reduction and the mild oxidation processes. The procedure and the equipment used for the film preparation were described in detail to establish reproducibility on the measured value.