Structure of iron oxide films prepared by evaporating various iron oxide powders

Crystalline films composed of mixtures (1) Fe, Fe₃O₄ and FeO, (2) FeO and Fe₃O₄, and (3) Fe₃O₄ were obtained by evaporating FeO powder (1) in a vacuum of 10⁻⁵ Torr; (2) in an oxygen atmosphere of 10⁻⁴−10⁻³ Torr; and (3) in an oxygen atmosphere of 10⁻¹ Torr, respectively. Films of γ-Fe₂O₃ were obtained by evaporating Fe₃O₄ powder in an oxygen atmosphere of 10⁻⁴ Torr, or by evaporating α-Fe₂O₃ powder in a vacuum of 10⁻⁵ Torr. The γ-Fe₂O₃ films gave only amorphous haloes in electron diffraction patterns. High resolution electron microscope images of the films showed crossed lattice fringes (whose spacings were assigned to the γ-Fe₂O₃ crystal) in areas 2 nm in extent. The formation of various iron oxide films is discussed in connection with experimental results from the oxidation of iron.