Molecular conformation changes in alkylthiol ligands as a function of size in gold nanoparticles: X-ray absorption studies.

J.M. RAMALLO-LOPEZ; L.J. GIOVANETTI; F.G. REQUEJO; S.R. ISAACS; Y.S. SHON; M. SALMERON

PHYSICAL REVIEW B - CONDENSED MATTER AND MATERIALS PHYSICS

APS

Lugar: Ridge, NY ; Año: 2006 p. 73410 - 73410

0163-1829

The bonding of hexanethiols to gold nanoparticles of 1.5, 2.0 and 3 nm was studied using X-ray Absorption Near Edge Spectroscopy (XANES) and Extended X-ray Absorption Fine Structure (EXAFS). We found that a substantial fraction of hexanethiol molecules are weakly bound and can be removed by washing in dichloromethane. After removal of the weakly bound molecules the S K-edge XANES spectrum reveals peaks due to S-Au and S-C bonds with intensities that change as a function of particle size. We explain this as the result of distortions occurring in the molecules adsorbed on the smaller particles. The distortions arise from the poor packing due to the high curvature of the particles. In the same line, EXAFS results show that the smaller particles bind more molecules per Au atom than the larger ones, which is again interpreted as a result of the curved nature of the surface.