Insights into the Electronic Structure of Ceramics Through Quantitative Analysis of Valence Electron Energy-Loss Spectroscopy (VEELS)

The electronic structure of ceramics can be extracted quantitatively from the valence electron energy-loss spectroscopy (VEELS) of transitions between the valence and conduction bands. We obtained VEEL spectra of several ceramics (FIG. 1) with a VG HB501 dedicated STEM equipped with Gatan PEELS. Improved data acquisition and new methods of data analysis allowed us to treat the data fully quantitatively. The reliable and accurate removal of the zero loss peak was crucial because intensities at energy losses just above the band gap of the ceramic material have a large influence on the results. An asymmetric Pearson VII function was fitted into the zero loss peak up to an energy loss for which no transitions are expected (an energy smaller than the band gap of the ceramic) and then extrapolated to higher energies. This limits the analysis to non-metallic materials, exhibiting non-zero band gap energies. We are currently developing methods to perform the analysis on metallic materials, using ellipsometric data in the visible and extrapolate the energy-loss function to 0 eV and thereby remove the need for the no transition energy.