Measurement of the dielectric function of α-Al2O3 by transmission electron microscopy - Electron energy-loss spectroscopy without Cerenkov radiation effects

The dielectric function of alpha-Al2O3 was measured by electron energy-loss spectroscopy (EELS) coupled with the difference method. The influence of Cerenkov radiation was significant in measurements using a 200 kV transmission electron microscope (TEM) and the correct dielectric function could not be obtained using the conventional EELS procedure. However, a good agreement between the optical data and EELS for the dielectric functions was obtained via a 60 kV TEM. Combining EELS and the difference method, however, provided an accurate measurement of the dielectric function for alpha-Al2O3 even at an accelerating voltage of 200 kV. The combination of EELS and the difference method in the nano-beam diffraction mode could derive an accurate dielectric function with superior spatial resolution regardless of the occurrence of Cerenkov radiation. (C) 2016 Elsevier B.V. All rights reserved.