Phase control of iron oxides grown in nano-scale structures on FTO and Si(100): Hematite, maghemite and magnetite

• Nano structured hematite films can be grown at 300 °C.
• Oxygen and iron pentacarbonyl precursors grow films in a Stranski-Krastanov mode.
• The choice of carrier gas affect the chemical and structural composition of the films.
• The choice of substrate/carrier gas combination can yield magnetite, maghemite or hematite.
• The grown hematite on fluorine doped tin oxide is suitable for photoelectrochemical applications.

We demonstrate that iron oxide in the form of hematite, suitable as absorption material in photoelectrochemical cells, can be produced by pulsed chemical vapour deposition. By choosing carbon monoxide or nitrogen as carrier gases in the process the phase and granularity of the grown material can be controlled. The choice of carrier gas affect the decomposition rate of iron pentacarbonyl used as iron precursor. The iron oxide phase is also dependent on the chosen substrate, here fluorine doped tin oxide and crystalline silicon have been used. Regardless of the substrate nitrogen yields hematite, whereas carbon monoxide gives magnetite on Si and maghemite on fluorine doped tin oxide. A combination of Raman spectroscopy, X-ray diffraction, and hard X-ray photoelectron spectroscopy were used for characterization of the crystalline phase and chemical composition in the films. Scanning electron microscopy were used to visualise the deposited films' nano-structure.