Monitoring the formation of interface-confined mixture by photoelectron spectroscopy

We have investigated valence-band properties of Pt(111) surface covered by an Ag layer. Aside from showing significant changes in the $d$ bands and the $sp$-like Shockley-type surface resonance depending on the thickness of the Ag layer, our spectroscopic data suggest the formation of an Ag-Pt mixture that progressively develops at the interface upon increasing the annealing temperature of the sample. On a 2-ML system, the Shockley resonance band is partially occupied and exhibits a large Rashba spin-orbit splitting that can be described by a first-principles band-structure calculation based on multiple-scattering theory. For the interface alloy, we have used the coherent potential approximation, which is one of the best models among the so-called single-site (local) theory. We observe a shift of the Shockley resonance due to the alloying process at the interface that probably favors the formation of the well-known triangular reconstruction.

Figure 1

Valence-band spectra measured with HeI excitation energy on Pt(111) surface covered by Ag layers. The left panel shows the evolution of the $d$ bands with the film thickness, and the right panel illustrates the changes in the valence band of 2-ML Ag/Pt(111) upon annealing of the sample.

Figure 2

Surface resonance bands obtained by ARPES measurements (left panel) and by first-principles calculations (right panel) for 2 ML of Ag on Pt(111) surface. The ARPES data have been recorded at normal emission along the $\overline{\Gamma }$-$\overline{K}$ direction and at $T=50$ K with a photon energy h$\nu$ $=$ 20 eV. The photoemission calculations include a surface potential correction (more detail see text).

Figure 3

Normal emission spectra measured at 50 K on 2 ML of Ag/Pt(111) annealed at different temperatures, together with the spectrum of bare Pt(111) (shaded area) obtained by first-principles band-structure calculations that would show up in an inverse photoemission experiment.

Figure 4

Spectral functions for semi-infinite half-space configurations obtained by first-principles calculations on 2-ML Ag/Pt(111) system with different compositions at the interface. From left to right: 100$\%$ Ag in the first deposited Ag ML, 80$\%$ Ag with 20$\%$ Pt in the first deposited Ag ML, and fully 100$\%$ Pt replacing Ag in the first ML [corresponding to the 1-ML Ag/Pt(111) system].

Figure 5

Normal emission spectra obtained by first-principles calculations on 2-ML Ag/Pt(111) system with different compositions at the interface: (dark) 100$\%$ Ag in the first deposited Ag ML; (blue) 95$\%$ Ag and 5$\%$ Pt in the first deposited Ag ML; (red) 90$\%$ Ag with 10$\%$ Pt in the first deposited Ag ML; and (green) 80$\%$ Ag with 20$\%$ Pt in the first deposited Ag ML.