Aggregation of oligothio dendrimer-semi-capped nanoparticles on solid surfaces: Droplets and 'doughnuts'

We report a simple method of forming Au nanostructure arrays over large areas. A thin film of oligothiodendrimer-stabilised Au nanoparticles was prepared via spin-coating on a solid substrate. The morphology of the adsorbed thin films is found to be markedly sensitive to the hydrophobicity of the underlying substrate. Adsorption on hydrophilic surfaces (native oxide-terminated Si(1 1 1) and mica) results in the formation of spatially correlated droplet aggregates with an average diameter of ∼300 nm, an average height of ∼30 nm, and an average areal density of ∼3 x 108 cm-2. On a highly hydrophobic surface (H:Si(1 1 1)), however, the dendrimer-coated particles aggregate so that the average height and diameter of the clusters are much lower (∼5 nm and ∼100 nm, respectively) whereas the areal density is significantly higher (∼5 x 109 cm-2). Moreover, and importantly, there are key differences in the topography of the aggregates on the hydrophobic and hydrophilic surfaces. While for the hydrophilic surfaces the aggregates form droplets with an approximately hemispherical shape, on H:Si(1 1 1) the dendrimer-coated nanoparticles aggregate to form mesa-like or 'doughnut' features