Inter-atomic distance contraction in thiol-passivated gold nanoparticles

Size-dependent inter-atomic distance contraction was investigated by Extended X-ray Absorption Fine Structure in thiol-capped gold nanoparticles. A slight nearest-neighbor distance reduction was observed as a function of particle diameter (2–4 nm range) but, for all samples, it was less than 1%. This value contrasts with the larger effect expected and found in other systems, especially for the smallest particles (2 nm) where it is twice as small. Our analysis also points out a short metal–ligand bond, suggesting a rather strong surface interaction. We interpreted these results as a passivant effect where the metal–ligand interaction partially compensates the expected lattice contraction.