Electronic structures of Au–Al thin-film alloys by high-energy XPS and XANES

Abstract

The Auger parameter analysis in a conjunction with Au M 3-edge XANES has been used to obtain the electronic configurations for Al 2Au and Au 2Al alloys. The net electron transfer from Al to Au (0.13 e − for Al 2Au) has been estimated using the modified final state Auger parameter shifts in combination with the Thomas and Weightman model. The magnitude and direction of charge transfer appear to be in agreement with the differences in electronegativity values of the elements. Further, the opposite sign of the Auger parameter shift for Au and Al indicates that the Au core holes in the alloys are in a better screening environment than the core holes in pure Au while Al in the alloy environment is less screened. Au M 3-edge XANES has been used to probe the unoccupied densities of Au 5d states. The appearance of the white-line features in Al 2Au and Au 2Al indicates the loss of 5d electrons at the Au site due to the charge redistribution caused by intra- [Au(5d)→Au(6s, 6p)] and extra-atomic [Au(5d)→Al(3s, 3p)] orbital hybridization. Al 2Au exhibits an increased transfer of charge away from the gold compared to Au 2Al due to the greater availability of empty states in the Al valence band. In general, the net charge transfer from Al to Au was substantially compensated by the 5d electron depletion, which is responsible for the shifts of core-level and valence band to higher binding energy. Changes in observed plasmon loss structures could be related to the strength of Au–Al bonding resulting from the localization of valence electrons. This further gives a clear picture of the charge rearrangement between Au and Al during alloying.