Water-Mediated Assembly of Gold Nanoparticles intoAligned One-Dimensional Superstructures.

ThisArticle shows that water in ethanol colloids of gold nanoparticlesenhances the formation of linear clusters and, more important forapplications in electronics, determines their assembly on surfaces.We show by dynamic light scattering that ethanol colloids containmainly monomers and dimers and that wormlike superstructures are mostlyabsent, despite UV–vis evidence of aggregation. Water addedto the colloid as a cosolvent was found to enhance the number of clustersas well as their average size, confirming its role in linear self-assembly,on the scale of a few particles. Water adsorbed from the atmosphereduring coating was also found to be a powerful lever to tune self-assemblyon surfaces. By varying the relative humidity, a sharp transitionfrom branched to linear superstructures was observed, showing theimportance of water as a cosolvent in the formation of cluster superstructures.We show that one-dimensional superstructures may form due to long-rangemobility of precursor clusters on wet surfaces, allowing their rearrangement.The understanding of the phenomenon allows us to statistically alignboth clusters and resulting superstructures on patterned substrates,opening the way to rapid screening in molecular electronics. [ABSTRACT FROM AUTHOR]