No abstract

The electronic behavior of gold nanoparticles ͑NPs͒ of ϳ2 nm capped with dendrimer and thiol molecules was studied with Au L 3,2-edge x-ray absorption near-edge structure ͑XANES͒. The results reveal the tunability of the d-electron distribution in the Au NPs by selective capping. That is, that the Au atoms in the NPs gain 5d electrons ͑relative to the bulk͒ when capped with weakly interacting dendrimers and lose 5d electrons when capped with strongly interacting thiol molecules. A semiquantitative analysis of the d-charge ͑holes͒ distribution is presented. This work demonstrates the important role of the capping molecules in the d-charge distribution of Au NPs and the usefulness of XANES in probing the electronic behavior of transition metal NPs.

The Ca L 3,2 -edge XANES spectra of six calcium salts have been measured in both total electron and fluorescence yields using a high-resolution spherical grating monochromator. The compounds investigated were; CaF 2 , CaCO 3 , CaCl 2 ·2H 2 O, calcium phosphate, calcium glycerophosphate and calcium gluconate. We find that the fine structure of the Ca L 3,2 -edges for each compound is unique and relates to the local structure of the Ca atom. The implications of these results to the study of the structure of calcium binding sites in systems of biologically interest will be discussed.

No abstract

Utilizing porous silicon as a reducing agent and a substrate, gold complex ions [AuCl4]- were reduced from aqueous solution to produce nanoparticles of gold upon the surface of porous silicon. Scanning electron microscopy (SEM) was utilized to study the morphology of the porous silicon layers and the deposits of gold nanoparticles. It is found that preparation conditions have a profound effect on the morphology of the deposits, especially on porous silicon prepared from a p-type wafer. The gold nanoparticles, varying from micrometric aggregates of clusters of the order of 10 nm, to a distribution of nearly spherical clusters of the order of 10 nm, to strings of ~10 nm were observed and compared to bulk gold metal using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS). These techniques confirm and complement the SEM findings. The potential for this reductive deposition technique is noted.Key words: gold nanostructures, reductive deposition, porous silicon, morphology, X-ray spectroscopy.