Determination of the complex dielectric function of epitaxial SrTiO3 films using transmission electron energy-loss spectroscopy

Abstract

We have demonstrated that electron energy-loss spectroscopy in transmission electron microscopy is a useful technique for analysis of the high-frequency dielectric properties on a microstructural level. Compositional variations and interfacial elastic strain of epitaxial (001) SrTiO3 thin films had a small effect on the imaginary part, ε2, of the complex dielectric function, εr(E). Changes in the low-frequency dielectric function, between Sr deficient and stoichiometric films, were much larger compared to the changes in the high-frequency function. Improved film stoichiometry and absence of strain caused the absolute value of ε2 to approach that of a stoichiometric single crystal bulk sample. Simultaneously, the low-frequency dielectric function of the films improved. The electronic polarizability, αe, was also extracted from the dielectric function. Indications were found that strain and compositional deviations from the bulk value, resulted in decreased ability to withstand dielectric breakdown.