Nanoscale force induced size-selective separation and self-assembly of metal nanoparticles: sharp colloidal stability thresholds and hcp orderingElectronic supplementary information (ESI) available: Experimental procedures for the size-selective separation and self-assembly of AuNPs, supplementary information on the colloidal stability of AuNPs as a function of temperature, thiol-PEG-carboxyl surface coverage and ethanol content and SEM images of AuNPs. See DOI: 10.1039/c0cc02428g

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. A versatile nanoscale force induced size-selective separation approach and electrostatic self-assembly of gold nanoparticles into hcp structured networks were developed.