Morphology and surface-plasmon resonance of silver nanoparticles sandwiched between Si3N4 and BN layers

Abstract

Nanocermet trilayered thin films consisting of silver nanoclusters sandwiched between two dielectric layers (the buffer and the cap) have been synthesized by ion-beam sputtering with an alternate deposition of the metal and the dielectric species. The influence of the amount of silver, the nature of the buffer and the cap (BN or Si3N4), and a time delay before the cap deposition on clusters morphology and repartition have been investigated by transmission electron microscopy. It has been observed that the clusters display truncated ellipsoidal shapes in which the height to diameter ratio H∕D decreases as the amount of deposited silver increases. For a given amount of silver, this ratio is lower in the case of a Si3N4 cap, whatever the nature of the buffer. Two explanations are proposed to account for this “cap effect” on clusters morphology: the first one is based on a calculation of the H∕D minimizing the surface free energy of the clusters embedded between the buffer and the cap; the second one holds on the shape relaxation of the coalesced nonequilibrium clusters towards their equilibrium shape with the buffer, this process occurring until clusters are fully covered with the cap. Because of the higher deposition rate of Si3N4 compared to BN, a Si3N4 cap would allow a less efficient reshaping and consequently lead to flatter clusters. This explanation is supported by the temporal evolution of clusters morphology and repartition observed during the time delay before deposition of the cap. The evolution of the spectral position of the surface-plasmon resonance (SPR) of the trilayers as a function of their structure has also been investigated by optical transmittance measurements. The influence of cluster morphology, as well as the nature of the buffer and the cap on the SPR spectral position are discussed.

Advanced optical effective medium modeling for a single layer of polydisperse ellipsoidal nanoparticles embedded in a homogeneous dielectric medium: Surface plasmon resonances

“…The correlation between the in-plane projected shape of the NPs and their in-plane effective diameter was described successively by two correlation laws of different slopes (typical of those found in the literature for NPs grown by vapor deposition 48,49 ), which are displayed in Fig. 6(a).…”

“…It has been shown 48,49 that coalesced NPs embedded in a dielectric medium, grown by vapor deposition, present a polydisperse height distribution correlated to their in-plane size and inplane shape distributions [see Fig. 2(a)].…”

“…48,49 The general equations obtained in Sec. II (sets of coefficients A j,uv , B uv , F k,uv ) can be adapted to obtain simple formulas that take into account these features.…”

“…[42][43][44][45][46] In contrast, little has been done using the surface susceptibility method regarding polydisperse ellipsoidal NPs, 47 which are nevertheless frequently encountered in nanocomposite thin films. 48,49 Indeed, the GRANFILM code, 50 based on the Bedeaux and Vlieger's approach, only permits calculations for supported NPs with a revolution axis perpendicular to the substrate and ignores the effects of size and shape distributions, together with their possible correlations. Due to its complex parameterization, the implementation of the full polydisperse Bedeaux and Vlieger's model does not seem to be straightforward, thus making the development of more specific models desirable.…”

Selective Dichroic Patterning by Nanosecond Laser Treatment of Ag Nanostripes

“…[ 3,4 ] The control of the plasmon features such as spectral width, [ 5 ] position, [ 6 ] and shape [ 7 ] can be accomplished by different physical deposition routes [8][9][10][11][12] providing adequate growing conditions of metal nanoparticles (MNPs). Pioneer works in the 1990s showed the optical selectivity of elongated Ag deposits on SiO 2 with applications as optical fi lters for windows to control solar heat gain and glare, among others.…”