Characterization of nanocrystalline α-Fe ₂O ₃ thin films grown by reactive evaporation and oxidation of iron

Iron oxide thin films, with an α-Fe ₂O ₃ phase, were deposited by two techniques. The first was evaporation of iron in vacuum, followed by oxidation through annealing in air. The second was reactive evaporation of iron in an oxygen atmosphere. This was also followed by annealing in air. The structural, morphological and chemical properties of the films were investigated. All films were polycrystalline with nano-sized crystallites. Structural characterization showed that the films deposited by the first technique had to be annealed at 400°C to obtain fully oxidized α-Fe ₂O ₃. On the other hand, the films deposited by the second technique already had the α-Fe ₂O ₃ phase before annealing. Morphological analysis showed that the films deposited by vacuum evaporation had considerable surface roughness and grain sizes that monotonically increased with annealing temperature. However, reactively evaporated films had smoother surfaces and larger grains, with a maximum grain size obtained in the annealing temperature range 300400°C. Surface chemical analysis indicated that the surfaces of the films consisted of Fe ₃O ₄ and Fe ₂O ₃, although the latter oxide was the predominant one.