| Nanocomposite BN/Ag/BN and Si3N4/Ag/Si3N4 trilayers containing a similar amount of silver have been synthetized by alternate ion beam sputtering of the metal and dielectric species. Their optical transmittance spectra at oblique incidence for a p-polarized light present two surface plasmon resonance (SPR) bands which positions can be interpreted using the generalized Maxwell-Garnett model. It suggests that both trilayers contain oblate ellipsoidal metal clusters, with a flatter shape in the case of Si3N4/Ag/Si3N4, in qualitative agreement with the structural informations obtained from cross-section transmission electron microscopy (TEM) characterization. The average height-to-diameter ratio of the truncated spheroidal clusters observed by this technique is close to 1 (respectively 0.7) when they are embedded in a BN (respectively Si3N4) matrix. Consequently, the nature of the matrix plays a key role in determining clusters shape, which then influence the position of the SPRs. |
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