Nanoscale force induced size-selective separation and self-assembly of metal nanoparticles: sharp colloidal stability thresholds and hcp ordering.

A simple and versatile nanoscale force induced precipitation approach for the separation of gold nanoparticles (AuNPs) was developed. The AuNPs show sharp size-dependent colloidal stability thresholds as a function of salt concentration. Upon separation, the AuNPs were electrostatically self-assembled onto silicon substrates by fine-tuning interparticle and particle-substrate forces, forming 2D AuNP networks with a high degree of hexagonal closest pack (hcp) superstructures.