Iron Oxidation at the atomic scale: an In-situ environmental TEM/STEM study

Fe and Fe-oxide (FeOx) based nanoparticles (NPs) have shown promising applications in physical and medical sciences. These include magnetic storage devices, catalysis, contrast enhancement in magnetic resonance imaging and magnetic hyperthermia. These applications rely on the magnetic and catalytic properties of the NPs. In particular, the NP magnetic properties are strongly influenced by their stoichiometry and their crystalline structure. Understanding the Fe oxidation processes down to atomic scale is paramount for the control of NPs production. It has been previously shown that crystalline defects in magnetite (Fe3O4) thin films are detrimental for their overall magnetization. In our previous work on such films, we have shown that ex-situ annealing under a CO/CO2 gas mixture can successfully produce Fe3O4 thin film virtually defect free with bulk like magnetic properties. In the first phase of this project we will expand the gas capability of the York Environmental Scanning Transmission Electron Microscope (ESTEM) by implementing a CO/CO2 gas line that will add up to the existing O2, N2 and H2 ones. In the second phase the Fe-O phase diagram will be investigated in-situ for nanoparticles and thin films from room temperature to 1100C. The phase transformations between Fe-oxides phases and their stability will be explored at the atomic scale. In particular to understand the optimal conditions to produce single crystal, defect free and chemically ordered magnetite nanocrystal with improved magnetic properties. This research will provide a deeper insight in the oxidation mechanism, crystalline defect formation, and their relation to the magnetic properties to great advantage to the field of magnetism and catalysis with potential industrial applications.