(223c) Large-Scale Crack-Free Gold Nanoparticle Monolayers with Adjustable Electrical and Optical Properties

Gold nanoparticles are widely studied due to the ease of controlled synthesis, facile surface modification, and interesting physical properties. However, a technique for depositing large-area, crack-free monolayers on solid substrates is lacking. Herein we present a method for accomplishing this. Spherical gold nanoparticles were synthesized as an aqueous dispersion. Assembly into monolayers and ligand exchange occurred simultaneously at an organic/aqueous interface. Then the monolayer film was deposited onto arbitrary solid substrates by slowly pumping out the lower, aqueous phase. This allowed the monolayer film (and liquid-liquid interface) to descend without significant disturbance, eventually reaching substrates contained in the aqueous phase. The resulting macroscopic quality of the films was found to be superior to films transferred by Langmuir techniques. In addition, the interparticle spacing was adjustable from 1.4 nm to 3.1 nm using different length alkylamine ligands. Both the surface plasmon resonance (SPR) and the electrical conductivity of the films show a strong dependence on particle spacing. This approach allows the precise control of interparticle spacing over large-area NP films. The demonstrated self-assembly of the 2D NP superlattice could have an impact on the manufacture of high performance optical and electronic devices.