Mechanism of the formation of copper-containing fractal-like crystallites in metal-organic thin films: Shape simulation and XANES analysis

Copper-containing thin films were synthesized by a citrate sol-gel method using ethylene glycol. The evolution of the shape and local atomic structure of the copper-containing fractal crystallites at different stages of growth was investigated by the combination of experimental and theoretical techniques. A surface morphological study of the deposited film samples was carried out using SEM. It revealed the evolution of the crystallite structures as a function of annealing temperature. To describe this mechanism diffusion-limiting aggregation and cluster-cluster models were used. X-ray absorption spectroscopy (XANES) was applied to show the dynamics of the local atomic structure of Cu ion and the copper oxidation state at different stages of crystallites formation. It was found that at temperatures up to 250 degrees C the Cu2Cl(OH)(3) (atacamite phase) and chelate complex are formed. With temperature increases changes in the local atomic structure as well as in morphology take place and at 500 degrees C CuO formed. As a result of these processes, the fractal organization of the other level was observed.