The effect of the addition of copper to iron (and vice versa) is investigated by creating either alloys single layers or stacks of copper and zinc layers with different thicknesses on a glass substrate. The experimental device consists in using an Ar-O₂ microwave plasma. Active species exit the reactor through a tiny hole (500 µm in diameter) and react with the copper-iron film to perform the direct synthesis of oxide nanostructures in a single step without any template or surfactant. The morphology, shape and size distribution can be controlled by varying the experimental parameters such as the amount of oxygen injected in the plasma, the microwave power, the treatment time or the alloy composition. It appears possible to synthesize different kinds of nanostructures with good reproducibility in a single-step process: nanowires, nanowalls or nanoblades. Various characterization means, including SEM, SIMS, TEM and XRD were used to determine the composition of the nanostructures. Besides, XPS microscopy experiments were carried out with the SPEM at the spectroscopy for chemical analysis (ESCA) microscopy beamline at the Elettra synchrotron facility in Trieste. We show that both oxides, CuO and Fe₂O₃, can be formed on the same spot (see figure). Furthermore, by controlling the composition of the alloy, we show that very thin CuO nanowires (with diameters as small as 5 nm) can be grown. Ultra-thin nanoblades of Fe₂O₃ can be formed. They are so thin than their edge is submitted to grow instabilities and become serrated.

The formation mechanism of these structures was investigated. The role of the addition of a new element on the growth mechanism, together with the way it is distributed within the stack, will be discussed. The role of stress on grain size, grain boundaries and outward diffusion of metallic ions will be discussed. Results will be compared to those obtained by different groups via thermal oxidation. Finally, a growth model will be proposed to explain the synthesis of the as-grown nanostructures.