Angle-Resolved Energy-Loss Spectra of Gd2O3

Energy loss spectra of heavy rare earths oxides show two well defined plasmon-like peaks below 40 eV and some intensity variation beyond. Since the high-energy maximum is at about twice the energy as the low-energy maximum, double scattering contributions may mask the former. This effect induces artifacts when one attempts to determine the dielectric function ε(ω) from Kramers-Kronig-analysis (KKA) of the loss spectrum. Knowledge of ε(ω) allows to heuristically assign interband transitions or plasma excitations to particular maxima. Measurements in diffraction mode allow detection of dispersive features in ε(ω,q).Polycrystalline Gd2O3-films of of 40 nm thickness were investigated at 120 kV in a Philips EM420, attached to which is a Gatan 607 Spectrometer. Spectra were taken in diffraction mode (image coupling) at 8 scattering angles with a q-resolution of ≈ 0.03 Å-1. Energy resolution was ≈ 2 eV. The spectra were combined to a q-dependent loss function, using aperture correction.