Structure and self-assembling of Co nanoparticles

In this work layers of colloidal nanoparticles obtained by thermolysis of Co2(CO8) were deposited on substrate surface by drying a drop in air eventually combined with the application of a magnetic field, or by spin coating. The formation of arrays of particles on Si substrates covered by Si3N4 layer was studied by high-resolution scanning electron microscopy and particle arrays on carbon coated copper grids by transmission electron microscopy. The crystalline structure of Co particles and its temperature evolution were analyzed by X-ray diffraction in situ in He gas and ex situ in UHV up to 700 °C. Two-dimensional (2-D) arrays of particles were formed by different types of preparation. The most regular ordering was obtained with the application of magnetic field perpendicular to the substrate surface, where 2-D hexagonal ordered arrays with length and width both between 200 and 500 nm were observed. In external magnetic field also three-dimensional arrays of nanoparticles–columns were formed. In the as-deposited state the nanoparticles show a poorly developed fcc crystalline structure. Most significant structural changes appear in the temperature range 400–450 °C where a well-developed fcc Co phase forms.