XPS and DFT studies of the electronic structures of AgAuS and Ag3AuS2

X-ray photoelectron spectra of core levels and the valence bands were acquired, and the density-of-states (DOS) were calculated using periodic density functional theory (DFT) for synthetic ternary compounds AgAuS and Ag3AuS2, known as minerals petrovskaite uytenbogaardtite, respectively, for the first time. The chemical shift of the Au 4f binding energy as large as 0.65 eV relative to bulk elemental gold was found for Ag3AuS2, in contrast to only about 0.3 eV for AgAuS. The DFT analysis showed, in particular, that the S 3p states are largely pushed out from the Ag 4d and Au 5d bands affording two sub-bands in the valence region of both substances, but the overlapping of the S 3p and Au 5d states is larger for Ag3AuS2. It was demonstrated that the energy position of Au 4f levels is mainly influenced by Au-Ag interaction, and increasing the number of Ag atoms in the first coordination shell of S-Au-S units on going from AgAuS to Ag3AuS2 results in the positive shift of the Au 4f bands consistent with the experimental data.