Kinetics and Mechanism of Nucleation, Growth and Stabilization of Metal Oxide Nanoparticles
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Kinetics and Mechanism of Nucleation, Growth and Stabilization of Metal Oxide Nanoparticles Rina Tannenbauma*, Scott Kinga, K. Hyunhb, Melissa Zubrisa and Nily Danc a School of Materials Science and Engineering, Georgia Institute of Technology Atlanta, GA; bDepartment of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN; cDepartment of Chemical Engineering, Drexel University, Philadelphia, PA. (*[email protected]) ABSTRACT Reactive metallic fragments that are formed by the decomposition of organometallic complexes, undergo a nucleation and growth process that gives rise to the formation of nanocrystals. In the absence of stabilizing molecules, the aggregation process is restricted mainly due to 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 surface adsorption of the polymer chains, 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 considered to represent the overall rate of the process. Moreover, it has been implicitly assumed that the formation kinetics of the metal nanoclusters directly coincides with the decomposition kinetics of their precursors. In this study, we attempt to decouple the kinetic characteristics of the various steps that comprise the overall nucleation and aggregation process cobalt oxide nanoclusters. A combination of infrared and x-ray photoelectron spectroscopies, and particle size determination by dynamic light scattering, are used to identify the individual contribution of each step to the overall mechanism of metal nanocluster formation. INTRODUCTION The physical and chemical properties of metal nanoclusters are determined to a considerable degree by their equilibrium size [1-5]. Since the design and fabrication of materials with nanoscale dimensions require the control of both their size and stability, methods of particle stabilization are of great interest. One of the most successful methods in this area has been the process of decomposition of organometallic complexes under controlled conditions in the presence of stabilizing polymer molecules, via a wellestablished procedure [6-9]. The formation of nanocrystals by the thermally-induced decomposition of organometallic precursors occurs via a nucleation and growth process involving highly reactive, coordinatively unsaturated metallic fragments, i.e. metallomers. In the absence of stabilizing molecules, the aggregation process is restricted by the decreasing mobility and diffusional rates of the particles as a function of their increasing size. In the presence of a p
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