Experimental and theoretical electronic structure determination for PtSi

We present a complete experimental and theoretical electronic structure study of PtSi using a combination of synchrotron radiation photoelectron spectroscopy (SR-PES), soft x-ray emission spectroscopy (SXE), x-ray absorption spectroscopy (XAS), and first principles electronic structure calculations. We have carried out both SXE and XAS measurements of the Si $L_{2,3}$ edge, which probe the Si $3s$ and $3d$ partial density-of-states (PDOS) in the valence and conduction bands, respectively. We have also obtained SR-PES data at photon energies of 80 and 130 eV for the valence band of PtSi. By taking advantage of the Cooper minimum effect we are able to probe the contribution of the Pt $5d$ orbitals. As an aid to interpreting the experimental spectra we have performed first principles calculations of the PDOS for the Pt $6p$ and $5d$ as well as the Si $3s,$ $3p,$ and $3d$ orbitals. We have carried out core-level PES measurements for Pt $4f$ and Si $2p$ and find a double shift in which both core levels are shifted to higher binding energy. First principles calculations confirm the presence of this double shift. Our combined experimental and theoretical results lead us to conclude that the Pt $5d$ orbitals are not highly localized as has been assumed in all previous experimental studies of PtSi. Rather we find that the influence of the $5d$ orbitals extends throughout the whole valence band and that the nature of the chemical bonds is more complex than the earlier studies have assumed. Our first principles calculations of the energy-resolved electronic charge density confirm this interpretation.