Photoelectron-spectroscopy study of the electronic structure of Au and Ag overlayers on Pt(100), Pt(111), and Pt(997) surfaces

We have used photoelectron spectroscopy techniques [UPS (ultraviolet) and XPS (x ray)] to study the electronic structure of Au and Ag overlayers deposited on Pt(100), Pt(111), and Pt(997). Between 0 and 1 monolayer, the valence bands of Au and Ag show changes in the form of shifts of the most tightly bound peaks and the appearance of new structures around a coverage $\ensuremath{\bigominus}=1$ monolayer. The Au $5{d}_{\frac{3}{2}}$ peak shifts 0.6 eV towards higher binding energies when $\ensuremath{\bigominus}$ varies from 0.1 to 1 monolayer and 0.5 eV more when $\ensuremath{\bigominus}$ varies from 1 to 6 monolayers. In the case of Au on Pt(100) a shallow minimum in the work function around $\ensuremath{\bigominus}=1$ monolayer is observed. The $4f$ core levels of Au on Pt(100) shift also to higher binding energy as $\ensuremath{\bigominus}$ increases. From $\ensuremath{\bigominus}=0 \mathrm{to} 1$ monolayer the shift is 0.6 eV and from $\ensuremath{\bigominus}=1 \mathrm{to} 4$ monolayers additional 0.4-eV shift is observed. These shifts are explained as due to the changing contributions of the Au atoms in island edges for surface ($\ensuremath{\bigominus}<1$) and bulk ($\ensuremath{\bigominus}>1$) coordination positions.