The role of solvents on the physical properties of sprayed iron oxide films

• Metastable iron oxide phases can be stabilized in sprayed films.
• Phonon modes are a function of thickness and chemical parameters.
• Maghemite can be stabilized in thinner films if organic solvents are used.

Iron oxide thin films were prepared by the spray pyrolysis technique using different solvents such as water, ethylene glycol/water, and ethanol/water. The properties of the films were studied by Raman spectroscopy, X-ray diffraction (XRD), atomic force microscopy and magnetometry. New results of the role of solvent on the growth and crystal structure of iron oxide films are presented. It was found that the solvent type affects the growth of iron oxide films, such as the deposition rate and the crystalline phase of the films. Additionally, it was revealed that the crystalline phase of the films depends strongly on the film thickness. Metastable phases such as oxyhydroxides and maghemite were found in thinner films while pure hematite was obtained in thicker films. It was detected that metastable phases can be stabilized in thinner films if organic solvents are used; particularly, single phase maghemite thin films can be obtained if ethylene glycol is used. The crystalline structure determined by Raman and XRD correlates very well with the magnetic properties of the iron oxide films; i.e., the canted ferromagnetic in hematite films and the ferrimagnetic character of maghemite were detected.