We show that the clusters formed by the irreversible aggregation of uniform aqueous gold colloids exhibit dilation symmetry and are well described as fractals with a Hausdorff or fractal dimension of ~1.75. The detailed structure of the clusters is studied with transmission electron microscopy, and is confirmed with small angle neutron scattering. The value of the fractal dimension obtained is in excellent agreement with that predicted by theory and computer simulation for cluster-cluster aggregation. We also discuss preliminary measurements of the kinetics of aggregation, which indicate that there are two limiting regimes with substantially different behavior. One is dominated by the particle-particle sticking time leading to relatively slow growth initially, but an increasing rate of growth as the aggregation proceeds. In contrast, the other is dominated by the diffusion time for clusters to collide leading to much faster aggregation, but with a decreasing rate of growth as the aggregation proceeds.

We study the dynamics of diffusion-limited cluster-cluster aggregation of aqueous colloids using quasielastic light scattering. Scaling behavior is found for the dependence of the mean cluster size on both time and initial concentration, and limits are placed on the scaling exponents of the cluster mass distribution. The fractal nature of the resultant clusters directly affects the exponents, illustrating the inherent relationship between the dynamic and static properties of kinetic aggregation processes.

We use transmission-electron micrographs to study the structure formed by the irreversible kinetic aggregation of uniformly sized aqueous gold colloids. The structures are highly ramified and exhibit a scale invariance that is well described as a fractal with a Hausdorff dimension of ∼ 1.75. This value is in excellent agreement with recent computer simulations of diffusion-limited aggregation when the clusters themselves are allowed to aggregate.

Detailed measurements of the photochemical and photophysical properties of an adsorbate on discontinuous metal‐island films are used to explore the unusual electrodynamics near rough metal surfaces. Several aspects of the properties have been measured: the magnitude the temporal decay of the fluorescence, the shape and temporal evolution of the fluorescence spectrum, and the effects on the spectrum of a photochemical hole‐burning process. Dramatic increases in the fluorescent decay rate and decreases in the photochemical reaction rate as well as systematic spectral shifts of the emission of molecules experiencing the different electrodynamic environments on the island film are observed. These results reveal the strong effects of the coupling between the adsorbate and the plasma resonances localized on the islands of the film. We model our results using the electrodynamic picture which has successfully described many aspects of surface‐enhanced Raman scattering and other optical processes on island films. The excellent agreement between this model and our results suggests that an important feature of the electrodynamics at these rough metal surfaces is the dipolar character of the couplings between the surface, the adsorbate, and the optical fields.

The unusual luminescent and photochemical properties of molecules near rough metal surfaces have been measured and used to ellucidate the electrodynamics at these interfaces.

The role of the electronic-plasma-resonance absorption of surface microstructure in the visible and UV pulsed laser desorption of adsorbates on a silver surface is examined. It is shown that the surface microstructure aids in the absorption of a significant fraction of the laser radiation and can lead to a relatively gentle thermal desorption of molecular monolayers absorbed on the metal. This substantially increases the sensitivity and selectivity of time-of-flight mass spectrometry in the analysis of adsorbates on the metal surface.