Dielectric response of small metal particle composites

The authors report the first measurements of the dielectric function for well characterised metal-insulator composite materials. These composite materials were prepared by a novel sputtering method and consist of uniformly sized (nanometre diameter) metal spheres embedded in the insulator matrix. The dielectric functions were measured by electron energy loss spectroscopy (EELS) and optical methods over the energy range 0.4 to 40 eV. No existing theory satisfactorily explains the results.