Interfacial Electronic Structure of a Near S11 Grain Boundary in a-alumina

Interband electronic structure of a near S11 grain boundary in a-alumina determined by spatially resolved valence electron energy-loss spectroscopy

Harald Müllejans* and Roger H. French**

*Max-Planck-Institut für Metallforschung, Institut für Werkstoffwissenschaft, Seestraße 92, D-70174 Stuttgart, Germany

**DuPont Co. Central Research and Development, Experimental Station, P.O. Box 80335 Wilmington, Delaware 19880-0356, USA

short title: Interband electronic structure of an alumina grain boundary

Abstract

            Valence electron energy-loss spectroscopy in a dedicated scanning transmission electron microscope has been used to obtain the interband transition strength of bulk a-Al₂O₃.  The interband electronic structure was obtained from critical point modeling.  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 S11 tilt grain boundary in a-Al₂O₃ were analyzed 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 S11 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. 

Figure 4.  Critical point models of the Interband Transitions from STEM VEELS data of a-Al₂O₃, showing the critical point set corresponding to the interband transitions from the O 2p bands, Al=O hybridized bands and the O 2s lower valence bands to the Al conduction bands.  Critical point model is fit to a) a-Al₂O₃ bulk grain and b) the a-Al₂O₃ near S11 tilt grain boundary. 

Figure 5.  Partial optical sum rules of the Interband Transitions of a-Al₂O₃ fit to STEM VEEL spectra, showing electron occupancies for the critical point sets corresponding to the interband transitions from the O 2p bands, Al=O hybridized bands and the O 2s lower valence bands to the Al conduction bands.  Partial optical sum rules are compared for the a-Al₂O₃ bulk grain and the a-Al₂O₃ S11 grain boundary. 

Comment: (c) 2009 Roger H. French , frenchrh@lrsm.upenn.edu
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