Optical Properties of Au−Ag Nanoboxes Studied by Single Nanoparticle Spectroscopy

The optical properties of two Au−Ag nanobox samples with average edge lengths of 44 and 58 nm and wall thicknesses of 6 and 8 nm, respectively, have been studied by single particle spectroscopy. The measurements gave an average line width of Γ = 306 ± 7 meV with a standard deviation of σ = 30 meV for the 44-nm boxes, and Γ = 350 ± 9 meV with σ = 35 meV for the 58-nm boxes. These line widths are much broader than those of gold nanorods with comparable resonance energies. The increased broadening is attributed to a combination of surface scattering of electrons, as well as increased radiation damping for the nanoboxes. Discrete dipole approximation calculations have been performed with and without surface scattering of electrons to compare with the experimental spectra. The calculations confirm that both electron-surface scattering and radiation damping are important effects in this system.