Investigations on phase transitions within thin Al 2O 3 layers on NiAl(001) — HREELS on aluminum oxide films

Abstract

We have investigated the phase transitions and the structure of thin aluminum oxide layers on NiAl(001) using high-resolution electron energy loss spectroscopy (HREELS), low-energy electron diffraction (LEED) and Auger electron spectroscopy (AES). The oxide films were prepared either by oxygen adsorption at 300 K and annealing to different temperatures or by oxidation at different temperatures up to 1500 K. We have demonstrated that in connection with LEED and AES data the HREEL spectra allow the determination of the structure of the alumina layers. Different phases of the Al 2O 3 layers have been observed depending on annealing or oxidation temperature. The observed energy losses are high-frequency branches ω + of Fuchs-Kliewer (FK) surface phonons. Calculated spectra based on dielectric theory reproduce the measured spectra very well. The thickness of the well-ordered θ-Al 2O 3 layer is estimated to be about 10 Å.