Enhanced Ordering in Gold Nanoparticles Self-Assembly through Excess Free Ligands

Self-assembly of nanometer-sized particles is an elegant and economical approach to achieve dense patterns over large areas beyond the resolution and throughput capabilities of electron-beam lithography. In this paper, we present results of self-assembly of oleylamine-capped gold nanoparticles with 8.0 +/- 0.3 nm diameter into densely packed and well-ordered monolayers with center-to-center distance of similar to 11 nm. Self-assembly was done in a Langmuir-Blodgett trough and picked up onto Si substrates. The nanopartides undesirably assembled within micrometer-sized droplets that were organic in nature. However, within these droplets, we observed that the addition of the excess ligand, oleylamine, drastically enhanced the self-assembly of the nanoparticles into monolayers with near-perfect ordering. This approach has the potential use in templated self-assembly of nanopartides for rearranging poorly ordered assembly into a commensurate prepatterned substrate.