Incorporation of Potassium at the Pt(111) Surface

Using electron-energy-loss spectroscopy and scanning tunneling microscopy, we find that at room temperature the binding site of K at the Pt(111) surface changes with increasing coverage. At low coverages, K adsorbs at surface hollow sites, forming an ionic bond with the substrate. Above a coverage of 0.1 monolayers, we observe a slow migration of K to subsurface binding sites in the second Pt layer. The measured vibrational frequencies are in quantitative agreement with cluster calculations for the proposed surface and subsurface bonding geometries.