Adsorbed rare-gas layers on Au(111): Shift of the Shockley surface state studied with ultraviolet photoelectron spectroscopy and scanning tunneling spectroscopy

Abstract

The energetic position of the Au(111) Shockley surface state is compared before and after adsorbing different rare gas monolayers (Ar, Kr, and Xe). We used ultraviolet photoelectron spectroscopy (UPS) and scanning tunneling spectroscopy (STS) in combination to get more complete information by using the advantages of both methods. For determining the energetic position and the effective mass of the surface state in UPS an analytic mathematical method is used, which takes the finite angular resolution of the analyzer into account. We performed STS scans for the pure Au(111) surface as well as covered with a monolayer Kr and Xe. For an accurate analysis it is possible to use an extended Kronig-Penney model to take into account the influence of the $23\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ reconstruction. We found that the first monolayer of a rare gas induces shifts of around $50--150\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ increasing with the gas atomic number, whereas a second monolayer has only a small influence of about $3--18\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$. Using an image potential model it is possible to characterize these shifts qualitatively. For a semiquantitative analysis the phase accumulation model is applied. Within this model we can describe the experimental data roughly with a Coulomb potential changing in dependence of the electron affinity and the dielectric constant of the rare gas.