Ag-Si3N4 multilayers with nominal Ag thickness of 1 nm and Si3N4 thickness ranging from 3 to 12 nm were elaborated by dual ion beam sputtering. The nanocomposite films were analyzed by transmission electron microscopy, grazing incidence small-angle X-ray scattering and spectroscopic ellipsometry. Optical properties exhibit surface plasmon resonance (SPR) coming from an enhancement of the electrical field inside Ag nanoclusters. The SPR spectral position has been related to the oblate shape of the nanoclusters. Furthermore, it is shown that a modification of the magnitude of the multipolar electromagnetic interactions among clusters occurs when the in-depth dielectric separation of the Ag layers varies from H to 2H, where H is the height of the nanoclusters. (C) 2004 Elsevier B.V. All rights reserved.