Scanning tunneling microscopy and small angle neutron scattering study of mixed monolayer protected gold nanoparticles in organic solvents

Abstract

When a binary mixture of ligand molecules is used to coat gold nanoparticles, stripe-like domains can occur. These nanodomains confer nanoparticles unique structure-dependent properties. The domain structure has been characterized primarily using scanning tunneling microscopy (STM) in air and in vacuum. Here we show the first STM images of striped nanoparticles in a solvent, 1-phenyloctane. We achieve stable imaging conditions on dodecanethiol–hexanethiol (C12 : C6) 2 : 1 protected gold nanoparticles. These features are persistent across many images and retain their direction and overall morphology when recorded at different scan angles. We also perform small angle neutron scattering (SANS) on two hybrid C6 : C12 nanoparticle samples dissolved in chloroform. The hybrid nanoparticles have the same composition and size distribution as samples imaged with STM, but one of the two ligands (either C6 or C12) is deuterated. Low resolution models reconstructed ab initio by simultaneous fitting of the SANS data reveal striped patterns of C6 and C12 on the gold surface. We use image analysis to quantitatively compare STM and SANS data, achieving remarkable agreement. This is the first paper to compare evidence of the existence of stripe-like domains for particles in solution using two independent techniques, and we believe that a combination of STM and SANS could become a major approach to characterize mixed ligand nanomaterials in solution.