Surface core-level shifts for Pt single-crystal surfaces

The (111) and (110) surfaces of Pt, clean, oxidized, and covered by CO, have been investigated for surface $4f$ core-level binding-energy shifts. For the (111) face the surface $\mathrm{Pt}4f_{\frac{7}{2}}$ core level was shifted by 0.40±0.05 eV to lower binding energy relative to the bulk peak. On the (110)-(1×2) reconstructed surface similarly shifted peaks at 0.21±0.05 and 0.55±0.05 eV were observed. Chemisorbed carbon monoxide shifts the Pt(111) surface-related core level by 1.3 eV to higher binding energy. Formation of subsurface oxygen did not produce changes in the $\mathrm{Pt}\mathrm{}\left(111\right)4f_{\frac{7}{2}}$ core-level binding energies. The results obtained are explained and their possible implications are discussed.