Tuning the electronic behavior of Au nanoparticles with capping molecules

The electronic behavior of gold nanoparticles (NPs) of $\text{∼2\hspace{0.17em}}\mathrm{nm}$ capped with dendrimer and thiol molecules was studied with $\mathrm{Au}{\mathrm{\hspace{0.17em}L}}_{\text{3,2}}-\mathrm{edge}$ x-ray absorption near-edge structure (XANES). 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 $\text{5d}$ electrons (relative to the bulk) when capped with weakly interacting dendrimers and lose $\text{5d}$ electrons when capped with strongly interacting thiol molecules. A semiquantitative analysis of the d-charge (holes) 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.