EFFECT OF COMPLETE OXIDATION ON THE VIBRATIONAL PROPERTIES OF ALUMINUM-OXIDE THIN-FILMS - AN ELECTRON-ENERGY-LOSS-SPECTROSCOPY STUDY

The vibrational properties of ultrathin (815) aluminum oxide films deposited on a Mo(110) substrate are studied with use of high-resolution electron-energy-loss spectroscopy (EELS) under specular-scattering conditions. It is found that remarkable intensity changes in the low-frequency (400-cm-1) optical-phonon mode can be induced by varying the extent of oxidation in the thin film. Two types of characteristic phonon energy-loss spectra are obtained from EELS measurements, which correspond to Al-rich nonstoichiometric films and fully-oxidized aluminum oxide films, respectively. Conversion between the two types of oxide films can be achieved by chemical means. By means of combined EELS and Auger-electron-spectroscopy studies, spectroscopic criteria for complete oxidation are provided for the aluminum oxide thin films. Possible structure changes following the process of complete oxidation are discussed. © 1990 The American Physical Society.