Optical properties of cluster-assembled nanoporous gold films

Abstract

We report a spectroscopic ellipsometry investigation of the electronic and morphological properties of\ud cluster-assembled nanoporous metallic gold films deposited from a low-energy supersonic cluster beam. We\ud modeled the optical response of the medium by explicitly introducing a variable degree of porosity in the film\ud and finite-size effects due to the cluster nanometeric size. We deduced the characteristic size of the individual\ud clusters within the nanoporous structure and their depth-resolved arrangement. Comparison with independent\ud data available in the literature yielded extremely good quantitative agreement with the results extracted from\ud our model, in terms of the degree of porosity of the films and of their surface roughness. The cluster-size\ud distribution in the films obtained by the optical model matched extremely well the one obtained by atomicforce\ud microscopy on isolated clusters. This demonstrates that, though the clusters are in contact with one\ud another in the porous film, they retain their crystallographic individuality when assembled in three-dimensional\ud structures

Exploring the Optical and Morphological Properties of Ag and Ag/TiO2 Nanocomposites Grown by Supersonic Cluster Beam Deposition

“…Our nanogranular Ag and Ag/TiO 2 nanocomposite (Ag/Ti 50-50) films shows a typical surface roughness and porosity quite lower than the ones observed for other films deposited by SCBD, either the Au films analyzed by Bisio [39] or the bare TiO 2 films in the works of Singh [46] and Toccafondi [47]. This difference could be traced back to different growth parameters of the sources, mainly the type of carrier gas (Ar or He) and different carrier injection pressure in the ablation chamber, anyway a sound motivation for these differences needs further investigation.…”

“…The model of bulk Au optical constants was corrected by the size dependent term Δ ε , similar to that appearing in Equation (2), to obtain the model dielectric function for the Au NPs films and even possible gradients of film densities and surface roughness were considered by implementation of multiple BEMA layers model with different void factors [39]. …”

Yeast Cytochrome c Monolayer on Flat and Nanostructured Gold Films Studied by UV–Vis Spectroscopic Ellipsometry

“…at ψ plots acquired on bare ns-Au, substraterelated peaked features can be identified in the range below 450 nm. The steep slope in the 490-560-nm range in the vis-NIR spectral range is instead related to the presence of the gold nano-grains as already discussed for similar samples [13]. Adsorption of molecules induces small yet fully appreciable changes which are best viewed in Fig.…”

“…The nanostructured films considered here had a nominal thickness of ≈40 nm; SE checks confirmed this thickness suggesting a variability of ±15%. The asdeposited granular Au films exhibit a high nanoscale porosity and surface roughness [13][14][15]; their morphology is affected by ageing phenomena [14]. In this experiment, we used films a few days after production, whose ageing dynamics was sufficiently cold that variation of SE spectra was negligible in comparison of the molecular-induced changes in the time scale of the adsorption experiment.…”

“…In the same wavelength range δ values for nanostructured samples are neatly (and reproducibly) positive. The simple Cauchy simulations seem fully sufficient to rationalise this behaviour, suggesting that it is mainly related to the substrate optical properties in turn related to the relatively complex film morphology [13]. In the case of ns-Au it turns out therefore difficult to disentangle the tiny TL contribution.…”