Preparation and characterization of iron oxyhydroxide and iron oxide thin films by liquid-phase deposition

Abstract

Iron oxyhydroxide thin films have been prepared from the aqueous solution system of FeOOH–NH ₄ F·HF (aq.) with added boric acid by a novel liquid-phase deposition (LPD) method and is the first attempt to preparate iron oxide thin films by this method. A crystalline β-FeOOH thin film was formed directly on the substrate upon immersion into a mixed solution of FeOOH–NH ₄ F·HF and H ₃ BO ₃ . The orientation of the deposited film differed according to the concentration of H ₃ BO ₃ in the solution. When the concentration of H ₃ BO ₃ was >0.30 mol dm ^-3 , the β-FeOOH thin film was preferentially oriented in the [211] direction. The β-FeOOH thin film formed was transformed into α-Fe ₂ O ₃ upon heat treatment in air flow. The α-Fe ₂ O ₃ thin films obtained were oriented in the [110] direction. The F content of the as-deposited β-FeOOH film was ca. 15% F/Fe and was reduced to 0.19% upon heat treatment.