Soft X-Ray Emission Spectra and the Bonding of Aluminum

Abstract

The L2,3 soft x-ray emission (SXE) spectra of Al in metallic Al, Al-Mn alloys, dilute Al-Mg alloys, the intermetallic compounds LiAl and Ni3Al, the semiconducting alloy (Al-Ga)As and insulating Al2O3 are presented. The spectra provide a measure of the s-like partial density of states (PDOS) localized at the Al atoms and show prominant qualitative features that may be identified with each of the major types of bonding in solids, ie. metallic, covalent and ionic. The spectra of metallic Al and of the Al-Mn alloys have parabolic densities of states characteristic of nearly free electron PDOS's. Al in Mg alloys have metallic PDOS's with a strong enhancement of the low energy region of the spectrum which is associated with screening of the extra charge on the Al ion core. In LiAl, the Al has tetragonal local symmetry, the spectrum is similar to that of silicon and the bonding is a combination of covalent and metallic. In AlxGa1-x As alloys, the Al has tetragonal local symmety, but the spectrum is strongly modified from the characteristic covalent form by the presence of a strong ionic component in the bonding. Finally, the spectrum of Al2O3 shows features characteristic of localized electronic orbitals and ionic bonding