Abstract
We have examined both the structure and surface chemistry of gold clusters formed by the kinetic aggregation of colloidal gold particles. The highly disordered, ramified aggregates can be very accurately described as self-similar or fractal objects with a fractal dimension equal to 1.75. Spectroscopic studies performed with surface-enhanced Raman scattering (SERS), clearly indicate that colloidal gold surfaces are highly heterogeneous, consisting both of donor and acceptor sites which can be identified as Au(0) and Au(I). respectively. Aggregation occurs when negatively charged species are displaced from the gold surface by more strongly bound molecular adsorhates, with the rate determined by the nature and concentration of the displacing species. The new insights afforded by the fractal description of the structure of the aggregates and the SERS probe of the chemical nature of the colloid surface should lead to a more complete understanding of the basic mechanisms of colloid aggregation. This potential is illustrated with a quantitative description of the dynamics of aggregate growth measured by dynamic light scattering.
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