Comparative high-energy photoelectron diffraction study of Pt(111), Ni(111), andPt50Ni50(111)

We report new experimental results concerning high-energy photoelectron diffraction from Ni core levels in pure Ni(111), from Pt core levels in pure Pt(111), and from Pt and Ni core levels in ${\mathrm{Pt}}_{50}$ ${\mathrm{Ni}}_{50}$(111). We show that, qualitatively, the observed diffraction patterns may be easily interpreted when proper account is taken of the strong internuclear axis enhancement. This enhancement, due to the predominance of forward single scattering over multiple scattering and backscattering, is a characteristic of the high-kinetic-energy region. More quantitatively, we reproduce the experimental results by performing theoretical calculations based on the quasidynamical method. Furthermore, an estimation of the degree of Pt segregation in ${\mathrm{Pt}}_{50}$ ${\mathrm{Ni}}_{50}$(111) is deduced from this comparison between Pt(111), Ni(111), and ${\mathrm{Pt}}_{50}$ ${\mathrm{Ni}}_{50}$(111) diffraction patterns.