Optical anisotropy of organized silver nanoparticles in 2D superlattice

We compare the optical properties of spherical particles organized in a two -dimensional (2D) structure with disordered and coalesced particles. Both p article preparations were deposited on cleaved graphite substrates. When pa rticles are arranged in a hexagonal array, the optical measurements under p -polarization show a new high-energy resonance which is interpreted as a co llective effect, resulting from optical anisotropy due to the mutual intera ctions between particles. We support this interpretation by numerical calcu lations performed for finite-size clusters of silver spheres. For disordere d and coalesced particles, a low-energy resonance appears instead of The hi gh-energy resonance observed for spherical and organized particles. This is interpreted as optical shape anisotropy due to the asymmetrical shape of c oalesced particles. (C) 2000 Elsevier Science B.V. All rights reserved.