Ge-Ag interface at room temperature: An energy-dependent photoemission study

The electronic structure of the Ge(111)-Ag interface has been studied using synchrotron radiation photoemission of the valence band at $\mathrm{hv}$=40.8, 80, and 130 eV (Cooper minimum for Ag $4d$ electrons) and of the Ge $3d$ and Ag $3d$ core lines at $\mathrm{hv}$=120 and 450 eV, respectively. By using extensively the Cooper-minimum techniques it was clearly demonstrated that in the first monolayers (2-3) a strong chemical interaction takes place between Ge and Ag at room temperature with incorporation of Ag into the Ge surface lattice. Further Ag growth on top of the intermixed region follows the Stransky-Krostanov mechanism with almost pure Ag island formation. The present data constitute the first evidence of intermixing at the Ge-Ag interface.