Molecular conformation changes in alkylthiols ligands as a function of size in gold nanoparticles.

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

Stanford University, Stanford, California, USA

Congreso; 13th International Conference on X-ray Absorption Fine Structure; 2006

Stanford Synchrotron Radiation Laboratory

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). The XANES spectra revealed  that a substantial fraction of weakly bound hexanethiol molecules are present in addition to those forming covalent bonds with Au atoms. The weakly bound molecules can be removed by washing in dichloromethane. After removal of the weakly  bound molecules the S K-edge XANES reveals peaks due to S-Au and S-C bonds with intensities that change as a function of particle size. Au L3-edge EXAFS results indicate that these changes follow the changes in coordination number of Au to the S atoms at the surface of the particles. This higher accessibility for S atoms to bond gold atoms can be explained by the high curvature of small NP.