Shape control of gold nanoparticles by silver underpotential deposition

Four different gold nanostructures: octahedra, rhombic dodecahedra, truncated ditetragonal prisms, and concave cubes, have been synthesized using a seed-mediated growth method by strategically varying the Ag⁺ concentration in the reaction solution. Using X-ray photoelectron spectroscopy and inductively coupled plasma atomic emission spectroscopy, we provide quantitative evidence that Ag underpotential deposition is responsible for stabilizing the various surface facets that enclose the above nanoparticles. Increasing concentrations of Ag⁺ in the growth solution stabilize more open surface facets, and experimental values for Ag coverage on the surface of the particles fit well with a calculated monolayer coverage of Ag, as expected via underpotential deposition.