Surface structure of ultra-thin Al2O3 films on metal substrates

The surface structure of ultra-thin Al2O3 films on NiAl(110) and Ru(0001) w as investigated by using high-resolution electron energy loss spectroscopy (HREELS). On a semi-empirical basis, the three phonon loss features, v(1) ( 380 similar to 430 cm(-1)), v(2) (620 similar to 660 cm(-1)), and v(3) (850 similar to 900 cm(-1)), of crystalline Al2O3 films were assigned to collec tive excitations of the microscopic vertical stretching motion of in-phase O-Al layers and to the stretching motions of the tetrahedrally and octahedr ally coordinated Al-O species, respectively. To a good approximation, the d istinct observation of the v(1) mode in the HREEL spectra of Al2O3 films ca n be a sign for the synthesis of a vertically well-defined Al2O3 phase. The relative intensity between the v(2) and the v(3) loss features has been us ed to determine the most probable oxide structure, amorphous, transition, o r alpha-like, by using the relative site occupation ratio of Al3+ cations t o hexagonal closely packed O2- anions. (C) 2000 Published by Elsevier Scien ce B.V. All rights reserved.