Electronic properties of Pt in bimetallic systems: photoemission and molecular-orbital studies for PtAl surface alloys

The adsorption of Pt on polycrystalline Al leads to the formation of surface alloys. The electronic properties of these systems have been examined using XPS and ab initio SCF calculations. The PtAl surface alloys display a Pt(5d) band that appears at much higher binding energy (≈ 1.8 eV) than in metallic Pt. This is accompanied by positive shifts in the Pt 4f (≈ 1.2 eV) and Al 2s (≈ 0.2 eV) levels. The PtAl bond is complex, involving an Al(3s, 3p) → Pt(6s, 6p) charge transfer and a Pt(5d) → Pt(6s, 6p) rehybridization that localize electrons in the region between the two metal centers.