Solvent Control of Surface Plasmon Mediated Chemical Deposition of Au Nanoparticles from Alkylgold Phosphine Complexes

Bottom-up approaches to nano fabrication are of great interest because they can minimize material waste and fabrication time. To achieve these ends a new method of Au deposition has was developed using surface plasmon resonance of a Ag surface and MeAuPPh₃ as a Au precursor, which deposited sub 15 nm Au particles. In this work we investigate the mechanism of Au deposition using density functional theory. Particularly, we investigate the role of the Au organic ligands and solvent on the deposition process. Due to the large size of the PPh₃ group, and the binding between the solvent benzene molecules and the Ag surface, the MeAuPPh₃ precursor is unable to adsorb to the surface; rather the Au-P bond must dissociation in solution (Ea=39 kcal/mol) before the MeAu group can associate on the surface. If there were no solvent molecules on the surface the barrier would be <20 kcal/mol making the reaction active at room temperature. Once on the surface MeAu groups are can undergo ethane elimination and form surface Au atoms which can produce the Au nanoparticles. Overall, the solvent molecules direct the Au precursor to go through a higher energy reaction path which requires high temperature if the reaction is to proceed at a reasonable rate. This enables the deposition to be controllable by the light induced SPR heating of the surface and surrounding solution.