Sol-gel-derived iron oxide thin films on silicon: Surface properties and interfacial chemistry

Uniform high-quality iron oxide thin films can be formed from the spin coating of iron oxide/hydroxide sol-gels on a silicon substrate. Thermal processing of the films at temperatures of ∼300 °C results in the transformation of films into a ternary layered structure with iron oxide, Fe₂O₃, at the surface, characterized by Mössbauer spectroscopy, and reduced, metallic iron characterized by depth profiling of the surface by X-ray photoelectron spectroscopy as a function of Ar⁺ etching. Imaging of the etched surface by scanning electron microscopy reveals two distinct regions at the interface, nanoparticles that are very iron-rich separated by an unstructured region that is somewhat less iron-rich. The results demonstrate a synthetic protocol for the spontaneous formaton of a ternary layered structure from a simple one-step preparation.