Optical Properties of Small Metal Spheres: Surface Effects
David R. Penn, S Apell
It has been assumed that the optical properties of small spheres can be understood by means of a Drude dielectric function that incorporates a boundary scattering rate 1 / τs~=vF / R, where vF is the Fermi velocity and R is the sphere radius. An effective scattering rate 1 / τs=fvF / R is calculated and f is evaluated as a function of photon frequency. The largest contribution to f is due to the electron density profile of the sphere rather than the boundary scattering that is reduced an order of magnitude by electron screening.