Charge Flow anddCompensation in Gold Alloys

Measurements were made by x-ray photoelectron spectroscopy of the $4f$ level energies in Au and the $3d$ level energies in Ag with these elements in several forms: pure metals, Au-Ag alloys, Au${\mathrm{Al}}_{2}$, and Au${\mathrm{Ga}}_{2}$. Only very small core-level energy shifts are seen, even though existing M\"ossbauer isomer-shift data for Au show that there are differences in $s$ charge at Au sites such that one would anticipate substantial level shifts. These two sets of observations are interpreted within the framework of band theory to mean that when Au is alloyed with Ag, Al, or Ga, the flow of $s$ charge onto Au sites is accompanied by a compensating depletion of $d$ charge. The problems associated with relating chemical shifts in alloys to charge flow are considered in some detail. It is concluded that the ratio of $d$ depletion to conduction electron gain is 0.6 \ifmmode\pm\else\textpm\fi{} 0.2 in the case of ${\mathrm{Au}}_{0.5}$ ${\mathrm{Ag}}_{0.5}$, and similar behavior is encountered in other Au alloys.