Electronic Behavior in Alloys: Au-Sn

Charge-flow and valence-$d$-band behavior in Au alloys have been studied in the Au-Sn alloy system by x-ray photoemission measurement of the valence bands and of core-level energy shifts for both atomic species. Published Mössbauer isomer-shift data for these alloys indicate that there is significant valence $s$ charge increase at Au sites and a somewhat smaller decrease at Sn sites upon alloying. An analysis, which includes screening in the Coulomb interactions between valence and core electrons and which combines the Mössbauer and core-level photoemission data, has been carried out. The results indicate that there is little net charge flow between Au and Sn, i.e., that the increase of non-$d$ conduction-electron count at Au sites is almost entirely compensated for by a decrease in $5d$ count; a similar $s-p$ compensation occurs at Sn sites. Coulomb screening is important to this analysis and we have applied it to similar results reported by us previously in the AuAg alloy system. Substantial hybridization of the Au $d$ bands with the Au "$s$" and with Sn valence-electron states is exhibited by the valence-band spectra; and the extent of this hybridization with final states above the Fermi level is indicated by the observed depletion in $d$ count.