Interband electronic structure of a near-Sigma 11 grain boundary in alpha-alumina determined by spatially resolved valence electron energy-loss spectroscopy

Valence electron energy-loss spectroscopy in a dedicated scanning transmission electron microscope has been used to obtain the interband transition strength of bulk alpha-Al2O3. The interband electronic structure was obtained from critical point modelling. Comparison to established results from vacuum ultraviolet spectroscopy was used to improve the analysis of the energy-loss spectra and quantitative agreement between both methods was obtained. Spatially resolved measurements of a near-Sigma 11 tilt grain boundary in alpha-Al2O3 were analysed with the same procedure. This revealed an increase in the electron occupancy of the O 2p valence band to conduction band transitions which can be associated with an increased ionic character of the bonding at the grain boundary with respect to the bulk material. This is consistent with the results of other studies which determined the atomic structure and then calculated the electronic band structure of the same near-Sigma 11 tilt grain boundary. Quantitative analysis of valence electron energy-loss spectroscopy can be regarded as a new electronic structure tool for application to localized structures such as internal interfaces in our quest to better understand their micro- and macroscopic properties.