Self-Assembly and Ripening of Polymeric Silver−Alkanethiolate Crystals on Inert Surfaces

Abstract

We characterize and compare the reaction of alkanethiol with Ag continuous planar thin films and Ag islands on inert substrates. Ag islands generate a significantly larger (3-fold) amount of alkanethiolate than continuous Ag films at comparable conditions. The reaction with planar Ag thin films produces alkanethiol self-assembled monolayers (SAMs), whereas the reaction with Ag islands yields two dissimilar products depending on the size of the islands. Small Ag islands are more likely to be converted into multilayer silver-alkanethiolate (AgSR) crystals, while larger Ag islands form monolayer-protected clusters (MPCs). The AgSR lamellar crystals are initially small having only a few layers. However, during thermal annealing, ripening occurs that generates large AgSR lamellae having diameters of 1 microm and thickness up to 30 layers. Atomic force microscopy shows the single-layer step-heights of individual crystals which match the layer thickness obtained via X-ray diffraction analysis. The crystals have facets and flat terraces with extended area, and have a strong preferred orientation (010) normal to the substrate surface. The MPCs move laterally upon annealing and reorganize into a single-layer network with their separation distance approximately equal to the length of an extended alkyl chain.