Plasmonic and metallic optical properties of Au/SiO2 metal-insulator films

Abstract

In this paper, the optical properties and the growth mechanism of Au/SiO 2 metal-insulator films (MIFs) are investigated by combining ellipsometry and transmission electron microscopy. The ellipsometric measurements, analyzed by using effective medium theories, show that the growth mechanism involves a Volmer-Weber growth mode while the morphology and the optical properties of Au/SiO 2 MIFs are directly related to the percolation of the Au nanostructures. Indeed, below the percolation threshold of Au, the MIFs consist of ellipsoidal Au inclusions embedded in a SiO 2 matrix. These insulating films present anisotropic plasmonic properties, attributed to the asymmetric interactions between nanaoparticles (NPs), which can be modeled according to the interacted shape distributed nanoparticle effective medium theory. At the percolation threshold of Au, an insulator-to-metal transition is observed. The MIFs simultaneously exhibit plasmonic and metallic optical properties, which can be described by the Bruggeman theory. The density of free electrons increases and the MIFs become more and more conductive as the Au volume fraction increases. We also demonstrate that for a high Au volume fraction, Bruggeman and Maxwell Garnett theories converge toward the same results, suggesting that the film is composed of isolated SiO 2 inclusion embedded in a gold matrix.

Tunable Localized Surface Plasmon Resonance and Broadband Visible Photoresponse of Cu Nanoparticles/ZnO Surfaces

“…29 The formation of NP agglomerates, chains, or complex networks can also produce an important broadening and red-shift of the plasmon resonance. [30][31][32]24 In our case, the red-shift is obviously mostly related to NP coalescence and the decrease in the interparticular spacing, which strengthen the coupling between different NP as they get closer to each other. In case of samples grown with 5000 cycles, where particles as large as 257 nm are observed, the NP size can also contribute to this red-shift.…”

“…However, they still support a plasmonic mode as confirmed by the presence of the LSPR band in ε i . Therefore, this sample presents a hybrid behavior between a metallic and a plasmonic material . For the sample obtained at 10 000 cycles, ε r is also negative, but no plasmonic band is observed, indicating a metallic behavior.…”

“…Therefore, this sample presents a hybrid behavior between a metallic and a plasmonic material. 24 For the sample obtained at 10 000 cycles, ε r is also negative, but no plasmonic band is observed, indicating a metallic behavior. This result is expected since, in this case, a continuous metallic Cu film was formed, as verified by TEM and SEM micrographs.…”

“…For example, changes in the geometry of the NP from circles to pentagons or triangles produce a significant shift in the plasmon signal and a red-shift has been predicted when spherical particles become more oblate . The formation of NP agglomerates, chains, or complex networks can also produce an important broadening and red-shift of the plasmon resonance. − , …”

Roadmap of ellipsometric characterization of plasmonic nanoparticles

“…SE requires a modeling step to determine the real part and imaginary part of refractive index. SE was previously used to investigate the growth of metallic NPs on silicon [8][9][10][11] , or in a dielectric matrix [12][13][14][15][16][17] . However, classical modeling approach fails to extract information on the NP morphology.…”