AVS 46th International Symposium
    Applied Surface Science Division Tuesday Sessions
       Session AS-TuP

Paper AS-TuP22
Surface Limiting Factors of the Growth of Metallic Nanoparticles

Tuesday, October 26, 1999, 5:30 pm, Room 4C

Session: Poster Session
Presenter: R. Tannenbaum, Georgia Institute of Technology
Authors: R. Tannenbaum, Georgia Institute of Technology
H. Rotstein, Technion-Israel Institute of Technology, Israel
A. Novick-Cohen, Technion-Israel Institute of Technology, Israel
Correspondent: Click to Email
Chemical synthesis of metal clusters, unlike UHV methods, offers a great deal of flexibility in manipulating cluster properties, such as the oxidation state and the reactivity of the metal clusters due to particle size variations, all within the bounds of the nanoscale regime. Stabilization and control of the size of metallic colloidal particles are achieved in polymer solutions, due to the adsorption of the polymer to the coagulating metal fragments, to form a layer which separates the particles sufficiently in order to keep van der Waals forces below thermal energy levels. Among the most promising chemical avenues, is the thermal decomposition of metal carbonyls in the presence of polymers with relatively low reactivity (e.g. polystyrene) under controlled inert atmosphere, resulting in the formation of zero-valent metallic particles. During the decomposition reaction of the metal carbonyl precursors highly reactive intermediates are formed, resulting in two major subsequent reaction pathways: (a) Aggregation to form small clusters; and (b) Interaction with the polymer. The final particle size and particle size distribution will be a direct function of the various facets of this complex mechanism. For the growth of zero-valent cobalt clusters, there is an inverse correlation between cobalt cluster particle size and the polystyrene concentration in the reaction solution. The increase in the concentration of polystyrene in solution will result in an increase of the concentration of the adsorbed polystyrene layer, and hence a decrease in the final cobalt cluster size. The thickness of the adsorbed polymer layer is calculated by using a combination of TEM and STM measurements. The difference in the particle size diameters calculated by the two methods provide an indication of the thickness of the polymer layer. We will present working models for the correlation between the final cobalt nanocluster size and the extent of metal-polymer surface interactions.