Structural changes in gradient colloidal thin gold films deposited from aqueous solution

Pattern formation is investigated in a one-dimensional gradient prepared from an aqueous colloidal gold nanoparticle solution. The hydrodynamic process can be reconstructed by determining the prominent length scales and surface roughness in the dried gradient. The structural information is obtained using a combination of grazing-incidence small-angle X-ray scattering, which is a method of high-statistical relevance, and a moderate microfocused beam. This allows for scanning the gradient and to locally reveal the structure of the thin film. Our results, based on a simplified hydrodynamic model, indicate a system oscillating between depleted regions, nanoparticle domains and complete nanoparticle layers.