Electron‐Energy‐Loss Spectroscopy of Different Al2O3 Modifications II. Lineshape‐Analysis of Energy Derived Dielectric Function

The dielectric function ε(E) = ε1(E) + iε2(E) deduced from electron‐energy‐loss measurements of amorphous and polycrystalline γ‐ and α‐Al2O3 is investigated in the spectral range from 5 to 30 eV. A lineshape analysis applied to the energy derivative of the dielectric function gives parameters of an exciton and an M0‐singularity in the band‐edge region. At higher energies, a set of critical points is identified. The data are interpreted in terms of the electronic structure of Al2O3 with special emphasis on a comparison between amorphous and polycrystalline films.