Kinetics of nucleation, growth, and stabilization of cobalt oxide nanoclusters

Metallic fragments, or metallomers (similar to the "mer"-based nomenclature for polymers), formed via the decomposition of organometallic complexes, are highly reactive, generating a nucleation and growth process that culminates in the formation of nanocrystals. In the absence of stabilizing molecules, the aggregation process is self-restricting mainly because of the decreasing mobility of the particles and their declining diffusional rates as a function of their increasing size. On the other hand, in the presence of a polymer in the reaction medium, the growing metallic particles are stabilized by the adsorption of the polymer chains onto their surfaces, thus lowering their surface energy and creating a barrier to further aggregation. Studies of the nucleation and aggregation kinetics of metallic particles formed from the decomposition of organometallic precursors have been used to shed light on the mechanism of their formation. In these studies, the rate of decomposition of the precursor organometallic complexes used has been deemed representative of the overall rate of the process. Moreover, it has implicitly been assumed that the formation kinetics of the metal nanoclusters directly mirrors the decomposition kinetics of the precursors. In this study, we attempt to decouple the kinetic characteristics of the various steps that comprise the overall nucleation and aggregation process for cobalt oxide nanoclusters. A combination of infrared and X-ray photoelectron spectroscopies, transmission electron microscopy, and dynamic light scattering is used to identify the individual contribution of each step to the overall mechanism of metal nanocluster formation.