Anomalous infra-red absorption of nanocermets in the percolation range

Abstract

We present a two-dimensional simulation of the optical absorption of gold granular films, using a real space renormalization procedure. This numerical effective-medium theory takes into account the actual morphology of the films. Results are compared both with experimental measurements and with other theoretical predictions asserting that the optical properties around the percolation threshold cannot be described by an effective dielectric function. Nevertheless, we obtain a good agreement between simulations and experimental data, whatever the morphology and the concentration. It is concluded on both theoretical and experimental arguments that the IR absorption can be attributed to classical surface plasmon modes, generally situated in the visible spectral range for spheroidal inclusions, broadened here towards higher wavelengths due to the formation of fractal clusters of various sizes and shapes.

An Effective Medium Theory Description of Surface-Enhanced Infrared Absorption from Metal Island Layers Grown on Conductive Metal Oxide Films

“…Increasing the gold volume fraction has little impact on the reflectivity until a threshold of approximately f Au = 0.28 is reached. This marks the onset of a pronounced, broad-band drop in the interfacial reflectivity caused by the density of metal island films reaching a percolation threshold. , At metal volume fractions well beyond the percolation threshold ( f Au > ∼0.37), the optical properties of the EM layer are dominated by the contribution of the metal, and the interface is highly reflective over all wavelengths. The same general trends are observed for s-polarized light (Figure b), although the reflectivity changes are less pronounced.…”

Infrared Monitoring of Diamond Metalization

“…For the case of Al, the intersection of the curves at one certain average thickness (about 6 nm) indicates percolation of Al islands as observed for noble metals on various substrates. 9,15 To obtain the Drude parameters for continuous films from measured IR transmittance spectra, data analysis was performed using the commercial software package Scout 16 with the Drude-like dielectric function e(x),…”

Optically monitored wet‐chemical preparation of SEIRA active Au nanostructures

“…The 2D filling factors obtained from the SEM images are very high compared with calculations, [18] where for a 2D site percolation model on a square lattice the filling factor at percolation was p c = 0.5927. In an experimental study, [19] Au island films prepared by vacuum deposition had a filling factor at a percolation threshold of p c = 0.50 (annealed) and p c = 0.62 (non-annealed). Our films having much higher values of p as a result from the wet-chemical preparation method should be advantageous concerning the SEIRA activity because of the denser packing of the Au islands.…”