Sujet de stage / Master 2 Internship

Thin epitaxial iron oxides films (M1-3xFe2+2x O4 (with M= Co, Ni and Cu)) will be prepared by atomic oxygen plasma assisted molecular beam epitaxy and characterized. The reaction and modification of the surface with respect to different chemical environment (electrolyte, gaz pressure) will be studied in situ for different cationic composition.

Photo)electrolysis can be a solution to produce hydrogen or reduce CO2. In such device, the chemical reaction occurs at the interface between the electrode and the electrolyte. To improve performance it is necessary to characterize this interface in realistic conditions. In the ANR OPTYMAL project, we developped an experiment to study in situ the reactivity of solid electrodes with an aqueous electrolyte in different experimental conditions (pH, light, electric field, magnetic field, dissolved CO2 level ...). Therefore, we will be able to characterize the electronic structure and the crystallographic structure of the electrode after exposure. The most efficient (photo)anodes are obtained with metal oxides and among them iron oxides (hematite alpha-Fe2O3), maghemite (gamma-Fe2O3), spinel (CoFe2O4, NiFe2O4, CuFe2O4) are promising. In the LNO group at SPEC, we have been interested for several years in improving the properties of (photo) oxide-based electrodes. More precisely, epitaxial oxide thin films with controlled doping levels, defects, thicknesses and crystallographic structures were prepared by Atomic Oxygen plasma assisted Molecular Beam Epitaxy (AO-MBE) on single crystalline substrates. In the present internship we propose to prepare different oxide films of spinel structure with different composition: M1-3xFe2+2x O4 (with M= Co, Ni and Cu) on Pt(001). The crystal structure will be determined in situ by electrons diffraction (RHEED). The composition of the surface will be determined by Auger electron spectroscopy and photoemission (XPS), before and after different treatment (exposition to atomic oxygen, deposition of a drop of electrolyte). Photo-electrolysis properties (photo-current, efficiency) will be measured in white light and monochromatic light and correlated to reactivity measurements.

The candidate will cover ultra-high vacuum techniques associated with growth by molecular jet epitaxy (thin film deposition, in situ characterizations) as well as the electrochemical characterization of photoanodes. The multi-disciplinary nature of the subject will be highly instructive for the candidate. The layers developed during this internship are part of the group's long-term research program.

Contact: Helene Magnan (helene.magnan@cea.fr)