Ionic strength mediated self-organization of gold nanocrystals: An AFM study

The deposition of charge-stabilized colloidal gold nanocrystals on silicon substrates, derivatized with (aminopropyl)triethoxysilane (APTES), is studied using atomic force microscopy. The influence of ionic strength on the spatial distribution of gold nanocrystal assemblies is analyzed in terms of radial distribution functions. The minimum interparticle distance for these deposited particles with diameters in the low-nanometer range is shown to be tunable by varying the ionic strength of the solution from which the particles are deposited. The results are in line with previous work on considerably larger particles. Furthermore, because of the strong electrostatic interaction between the citrate-covered nanocrystals and the APTES-derivatized substrate surface, the sticking coefficient is one, while the surface mobility is negligible. In agreement with this, the results can be described perfectly in terms of the random sequential adsorption model for "soft" particles.