Characteristic energy-loss spectra of 20-keV electrons in amorphous and polycrystalline ${\mathrm{Al}}_2$${\mathrm{O}}_3$ have been measured in transmission at zero scattering angle. The dominant loss peak, due to plasmon excitation, occurred at 22.6±0.2 and 24.3±0.2 eV for the amorphous and polycrystalline films, respectively. Lower-lying weaker losses were observed at about 8.7 and 13.5 eV in both films, with an additional loss at 17.7 eV in the polycrystalline film. Using a previously developed technique, values of $-\mathrm{Im}{\epsilon }^{-1\mathrm{}}$ and electron-energy-loss oscillator strength were derived from the loss spectra. The results for anodized ${\mathrm{Al}}_2$${\mathrm{O}}_3$ are in excellent agreement with existing optical measurements.

• Received 9 August 1967

DOI:https://doi.org/10.1103/PhysRev.165.1067