title: Gold nanoparticles with different capping systems: an electronic and structural XAS analysis.
abstract: Gold nanoparticles (NPs) have been prepared with three different capping systems: a tetralkylammonium salt, an alkanethiol, and a thiol-derivatized neoglycoconjugate. Also gold NPs supported on a porous TiO(2) substrate have been investigated. X-ray absorption spectroscopy (XAS) has been used to determine the electronic behavior of the different capped/supported systems regarding the electron/hole density of d states. Surface and size effects, as well as the role of the microstructure, have been also studied through an exhaustive analysis of the EXAFS (extended X-ray absorption fine structure) data. Very small gold NPs functionalized with thiol-derivatized molecules show an increase in d-hole density at the gold site due to Au-S charge transfer. This effect is overcoming size effects (which lead to a slightly increase of the d-electron density) for high S:Au atomic ratios and core-shell microstructures where an atomically abrupt Au-S interface likely does not exist. It has been also shown that thiol functionalization of very small gold NPs is introducing a strong distortion as compared to fcc order. To the contrary, electron transfer from reduced support oxides to gold NPs can produce a higher increase in d-electron density at the gold site, as compared to naked gold clusters.
authors.affiliation: Instituto de Ciencia de Materiales de Sevilla, and Grupo Carbohidratos, Laboratory of Glyconanotechnology IIQ, CSIC-Universidad Sevilla, Américo Vespucio nr. 49, 41092-Sevilla, Spain.
authors.forename: C
authors.initials: C
authors.lastname: López-Cartes
authors.forename: T C
authors.initials: TC
authors.lastname: Rojas
authors.forename: R
authors.initials: R
authors.lastname: Litrán
authors.forename: D
authors.initials: D
authors.lastname: Martínez-Martínez
authors.forename: J M
authors.initials: JM
authors.lastname: de la Fuente
authors.forename: S
authors.initials: S
authors.lastname: Penadés
authors.forename: A
authors.initials: A
authors.lastname: Fernández