Phase Discrimination through Oxidant Selection in Low-Temperature Atomic Layer Deposition of Crystalline Iron Oxides

Control over the oxidation state and crystalline phase of thin-film iron oxides was achieved by low-temperature atomic layer deposition (ALD), utilizing a novel iron precursor, bis­(2,4-methylpentadienyl)­iron. This low-temperature (<i>T</i> = 120 °C) route to conformal deposition of crystalline Fe₃O₄ or α-Fe₂O₃ thin films is determined by the choice of oxygen source selected for the second surface half-reaction. The approach employs ozone to produce fully oxidized α-Fe₂O₃ or a milder oxidant, H₂O₂, to generate the Fe²⁺/Fe³⁺ spinel, Fe₃O₄. Both processes show self-limiting surface reactions and deposition rates of at least 0.6 Å/cycle, a significantly high growth rate at such mild conditions. We utilized this process to prepare conformal iron oxide thin films on a porous framework, for which α-Fe₂O₃ is active for photocatalytic water splitting