Reflection electron energy loss spectroscopy of nanometric oxide layers and of their interfaces with a substrate

The aim of the present work was to evaluate the ability of reflection electron energy loss spectroscopy (REELS) as a non-destructive method to obtain depth profiles of dielectric constants, in a complementary way to transmission electron energy loss spectroscopy (TEELS). Two prototypical samples were used: a SrTiO3 single crystal and a 2 nm thick SiO2 layer on a Si single crystal. The single scattering cross-sections were decomposed into bulk, surface and interface contributions, with Drude–Lorentz parameters of the dielectric function fitted on available optical or TEELS data. We show that the evolution of the shape of the REELS single scattering cross-section with primary energy is qualitatively well reproduced by our model. In the case of the 2 nm SiO2 layer on Si, introducing the Si/SiO2 interface energy loss function contribution proved necessary to account for the interface plasmon peak observed, in very good agreement with reported TEELS measurements. REELS is well suited to studying dielectric properties of interfaces between a substrate and a nanometric layer.