Final Activity Report Summary - AMMAN (Advanced Electron Microscopy Study of Magnetic Nanocomposites) This proposal applied advanced electron microscopy techniques to the study of magnetic nanocomposite materials, in particular manganese (Mn) and cobalt (Co) ferrite and iron-cobalt (FeCo) alloy nanoparticles in silica aerogel matrices prepared by a sol-gel method. The aerogel matrix is like a sponge which helps keeping the nanoparticles separated. The nanoparticles are so small that they display a new magnetic behaviour called superparamagnetism, and so these materials are promising for magnetic applications. In fact, the magnetic properties are keenly studied by collaborators of the project. What is very important for understanding the magnetic properties is a detailed knowledge of the arrangements of atoms within the nanoparticles. They have previously been studied using X-ray absorption spectroscopy which gave a detailed picture of the average arrangement of atoms. However, there were key questions about the homogeneity of nanoparticles in terms of whether the arrangement of atoms is the same in every nanoparticle, or there is a some variation, for example, whether the ratio of Fe to Co is always the same among nanoparticles. These questions could only be addressed by the application of advanced transmission electron microscopy techniques and this was the goal of the project. These microscopy techniques have the essential attribute of giving information about the arrangement of atoms within individual nanoparticles, rather than the average. High resolution electron microscopy (HREM) of nanoparticles showed them to be largely isolated crystal grains. Energy filtered imaging was used to create images which are sensitive to the distribution of Fe and Co, and these map variations in the Fe to Co ration among nanoparticles. However, the signal-to-noise from such small nanoparticles (approximately 5 nm) was at the limit of the capabilities of the technique. Hence another advanced microscopy technique, energy dispersive X-ray (EDX) spectroscopy in a scanning transmission electron microscope (STEM), was applied. Since the energy of X-rays is characteristic of the elements present, this provides another method to map variations in the Fe to Co ratio. The EDX results showed very good homogeneity for ferrite nanoparticles, but signs of inhomogeneity in FeCo nanoparticles. These results have laid the foundation for future microscopy experiments by the fellow and supervisor. During the project, the fellow received special training in these advanced electron microscopy techniques and associated data analysis, including the technique of HREM image simulation. Furthermore, the project provided a stimulating platform for extending the previous X-ray absorption spectroscopy expertise of the fellow. In particular, new X-ray Absorption Near Edge Structure (XANES) measurements provided an essential supplement to the information available from the microscopy techniques. Analysis of the XANES data revealed key details on the formation of CoFe2O4 nanoparticles in the aerogel SiO2 matrix. Hence the host institution proved a fertile environment for advancing the expertise of the fellow in multi-technique characterisation of nanostructured materials, to incorporate those advanced electron microscopy techniques.
