Extinction spectra of quasi-spherical silver sub-micron particles

In this paper, we present the experimental data on the extinction spectra of aqueous suspensions of silver sub-micron particles as well as those for planar arrays of particles. The spectra of noninteracting silver particles, i.e. colloidal suspension consist of two characteristic bands: dipole at 545 nm and quadrupole at 430 nm components of the surface plasmon resonance. Presence of some fraction of silver whiskers in colloids causes broadening and tailing of the dipole component. Coating of Ag particles with Si mantle shifts plasmon resonances to the longer wavelengths. The extinction spectrum of planar array of Ag sub-micron particles self-assembled on a glass substrate drastically differs from that for colloidal suspension. The effect may arise from coherent coupling of surface plasmons associated with the particles.