Formation and structure of a (√19 × √19)R23.4°-Ge/Pt(1 1 1) surface alloy

An ordered (√19 × √19)R23.4°-Ge/Pt(1 1 1) surface alloy can be formed by vapor depositing one-monolayer Ge on a Pt(1 1 1) substrate at room temperature and subsequently annealing at 900-1200 K. The long-range order of this structure was observed by low energy electron diffraction (LEED) and confirmed by scanning tunneling microscopy (STM). The local structure and alloying of vapor-deposited Ge on Pt(1 1 1) at 300 K was investigated by using X-ray Photoelectron Diffraction (XPD) and low energy alkali ion scattering spectroscopy (ALISS). XPS indicates that Ge adatoms are incorporated to form an alloy surface layer at ∼900 K. Results from XPD and ALISS establish that Ge atoms are substitutionally incorporated into the Pt surface layer and reside exclusively in the topmost layer, with excess Ge diffusing deep into the bulk of the crystal. The incorporated Ge atoms at the surface are located very close to substitutional Pt atomic positions, without any corrugation or "buckling". Temperature Programmed Desorption (TPD) shows that both CO and NO adsorb more weakly on the Ge/Pt(1 1 1) surface alloy compared to that on the clean Pt(1 1 1) surface.