Plasmonic excitations in ZnO/Ag/ZnO multilayer systems: Insight into interface and bulk electronic properties

Abstract

Electron energy-loss spectroscopy experiments in transmission were carried out on silver-based multi-layer systems, consisting of a silver layer of various thicknesses (8, 10 and 50 nm) sandwiched between two Al-doped ZnO layers. The films were produced by magnetron sputtering using potassium bromide single crystals as substrates. The electronic structure of these systems was probed and analyzed with respect to their plasmonic excitations, which can be basically split up into excitations of the electrons in the bulk silver and excitations at the ZnO:Al/Ag interface. A detailed examination of the momentum dependence of the plasmon peaks revealed a positive dispersion for both, the volume and the interface plasmon, where only for the first one a quadratic behavior (as expected for a free electron gas) could be observed. Furthermore, the peak width was analyzed and set into relation to electrical conductivity measurements by calculating the plasmon lifetime and the electron scattering rate. Here, a good agreement between these different methods was obtained.