Toward a universal extinction spectrum of self-affine silver colloid clusters: Experiment and simulation

Polarized extinction spectra of large fractal aggregates of colloidal silver deposited gravitationally onto a quartz substrate were measured by transmission as a function of angle of incidence. The spectral components tangential and normal to the average plane of the clusters compacted along the direction of deposition were extracted from these and compared with spectra calculated from simulated fractal aggregates that were projected onto a plane. The two sets agree acceptably, suggesting that the normal and tangential spectral components represent “universal,” i.e., size-independent extinction spectra characterizing all (compacted) cluster–cluster aggregates of colloidal silver.