Direct observation of the structure of gold nanoparticles by total scattering powder neutron diffraction

Fluorothiol-capped fcc gold nanoparticles, with a mean diameter of approximately 4 nm have been studied using total scattering powder neutron diffraction at 15 and 300 K on the NPDF diffractometer at the Manuel Lujan Jr. Neutron Scattering Center. The results are compared with bulk gold powder. A real space analysis of the structure of the nanoparticles has been performed using the pair distribution function (PDF). This provides valuable information and reveals several interesting features. The PDF pattern for the nanoparticles is significantly attenuated compared to bulk gold due to the finite size of the particles; the attenuation is consistent with the 4 nm size of the particles. The nanoparticles have a slightly smaller lattice parameter at both temperatures but the nearest neighbor Au–Au vectors are entirely symmetrical and there is no evidence for structural relaxation associated with atoms near the surface. The vector between surface Au atoms and sulfur of the thiol cap layer can be observed at ∼2.4 Å. The study points to the great power of total neutron scattering in ensemble-averaged analysis of structure in the nano regime.