X-ray photoemission spectroscopy of Pt-Cu: A canonical alloy

The possibility of employing x-ray photoemission valence-band spectra in a quantitative fashion for elucidation of valence-electron structure changes induced by alloying is examined. The special, or "canonical," property of ${\mathrm{Pt}}_{1-x}{\mathrm{Cu}}_x$, that one of the components, Pt, displays no measurable core-level shift, permits extraction of such changes from core-level and valence-band data alone. A relation between the $d$-resonant level shifts and the centroid of the valence-band spectra is derived and comparison of the centroid and core-level shifts leads to the desired information. The analysis indicates that there is no charge transfer in the system and that only Cu has significant valence occupation changes upon alloying, corresponding to dehybridization. Furthermore, information regarding Fermi-energy shifts is extracted and not required as input—the results suggest that the shifts of the Fermi levels cannot be identified with those of the work functions as in other work. Model calculations indicate that dehybridization is to be expected as an "antihybridization" effect for a narrow $d$-band metal in a wide $d$-band one.