Structural evolution of thiol-capped gold nanoparticle monolayers undergoing controlled nanowetting

Monolayers of thiol-capped gold nanoparticles characterized by a poydisperse/bimodal size distribution were prepared on silicon substrates and were subsequently wet by nano-thin liquid layers of solvents of varying quality. The structural changes were probed in-situ by synchrotron X-ray surface scattering. It is found that thin solvent films of thickness comparable to the nanoparticle size tend to improve the monolayer uniformity regardless of the quality of the solvent. On the other hand, thick films dissolve the monolayer if the liquid is a good solvent, while induce nanoparticle aggregation in the case of a bad solvent. The interplay of size-selective segregation and nanoparticle aggregation overcomes the intrinsically large polydispersity and leads to the formation of oriented colloidal crystallites.