| Abstract
| - Spectroscopic ellipsometry and atomic force microscopy (AFM) experiments are employed to characterizenanocolloidal gold films, self-assembled at APTES-derivatized Si/SiO2 surfaces. X-ray fluorescencemeasurements after deposition confirm that AFM provides a representative means to probe the absolutesurface coverage. Optical properties of gold nanocrystal assemblies are investigated both ex situ afterdrying and in situ prior to evaporation of the solvent. Quantitative optical characterization of these highlyinhomogeneous systems is not unambiquous. Conventional effective medium approximations are notapplicable to these systems. To enable an accurate analysis, extinction measurements on colloidal suspensionsare performed. The limited particle size in relation to the electron mean free path leads to a modificationof the dielectric function at longer wavelengths. Ellipsometry spectra of the colloidal gold films are analyzedqualitatively using an optical invariant and principal component analyses. Quantitative results are obtainedusing a theory which treats the nanocrystals as polarizabilities at the Fresnel interface. Above approximately20%, the coverages determined from optical spectra are in agreement with what is found from AFM images.At lower coverages, the optical results seem to overestimate the actual nanocrystal density. The discrepanciesare discussed in terms of image charge effects arising from the proximity of the substrate.
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