Self-assembly of TiO2 nanoparticles on native oxide terminated silicon surfaces

The TiO2 nanoparticle assemblies on native oxide terminated silicon substrates have been studied using Atomic Force Microscopy (AFM). The results lead to a consistent picture demonstrating the interplay between the coverage fraction of solvent and its thickness variation. Depending on this latter parameter, hole nucleation, multilayer-patterns, 3D structures, and nano-patterns ranging from isolated rings to cellular-like patterns were observed. Chemical potential as an explicit function of the remaining solvent coverage after initial solvent evaporation, potential gradient, capillary forces and surface instabilities driven by Laplace pressure are plausible factors to account for the observed patterns. The striking dependence of nanoparticles assembly on the layer thickness opens up a new parameter space in understanding the self-assembly mechanism of TiO2 nanoparticles.