Characterization of Au/Au Core/Satellite Particles Au/Au core/satellite particles, synthesized following the procedure illustrated in Figure , were characterized by UV/Vis extinction spectroscopy and scanning electron microscopy (SEM). UV/Vis extinction spectra of freshly prepared C/S particles show two equally intense maxima at 525 and 641 nm. The monomer band at 525 nm can be assigned to unbound monomeric particles. Most of the unbound particles are satellite particles (𝜆 𝑚𝑎𝑥 = 520 nm) since they were added in excess during synthesis in order to maximize the number of satellites per core particle.