Atomic and electronic structure of amorphous Al-Zr alloy films

Amorphous Al(73)Zr(27) alloy film, grown and then subjected to heat treatments at 400 and 700 °C, was studied using a combination of x-ray diffraction and soft x-ray spectroscopic techniques. The Al L(2,3) and Al K x-ray absorption spectroscopy (XAS) and Al L(2,3) x-ray emission spectroscopy (XES) used allowed probing the unoccupied and occupied Al 3s, d states and unoccupied Al 3p states in the sample studied. An irreversible transition from amorphous alloy to a mixture of polycrystalline alloy and amorphous alloy, and then to an amorphous oxide phase was observed. After the annealing at 400 °C the Al L(2,3) spectra obtained by XAS could be explained as sums of spectra from amorphous Al(73)Zr(27) alloy and (poly)crystalline Al. This indicates that the sample consists of a mixture of Al-rich crystalline and Zr-enhanced amorphous alloys, as compared to the stoichiometry of the as-deposited Al(73)Zr(27) sample, and that the electronic wavefunctions in the crystalline and amorphous regions can be considered to be confined within the respective regions. The relative amounts of Al atoms were found to be around 1:3 in the crystalline and amorphous phases, respectively, as deduced from the analysis of changes in the electronic structure using Al L(2,3) XAS data. The interpretation was confirmed by the Al K XAS and Al L(2,3) XES. Upon further annealing at 700 °C the polycrystalline phase transformed into amorphous oxide, while the amorphous alloy phase underwent gradual oxidation. The important finding was that the greater part of the sample remained in the amorphous state throughout the temperature regimes described.