Multiple-interface coupling effects in local electron-energy-loss measurements of band gap energies

Electron-energy-loss spectroscopy acquired with a subnanometer probe is used to record electron excitation spectra in a nanometer-scale layered structure. When applied to measure band gap energies in a HfO2 layer, we demonstrate that the desired local information is obscured by delocalized contributions from interface plasmons, interband transitions, and Čerenkov radiation. Simulations performed within a relativistic dielectric formalism, incorporating electromagnetic interaction between all layers in the investigated nanostructure, prove to be essential in identifying the various energy-loss signals, in particular, those associated with multiple-boundary effects.