SURFACE ALLOYING AT THE SN-PT(111) INTERFACE - A STUDY BY X-RAY PHOTOELECTRON DIFFRACTION

The formation of surface alloys obtained by annealing ultrathin films of Sn deposited on the Pt(111) surface was investigated by low energy electron diffraction and X-ray photoelectron diffraction. The Pt(111)( 2 x 2)-Sn and Pt(111)(square-root 3 x square-root 3)R30-degrees-Sn for m after deposition of amounts of Sn in the range from 0.2 to 1 ML and subsequent annealing at 1000 K are found by XPD to be single atomic la yer surface alloys. Depositing 4-5 ML of Sn and annealing at 400-600 K produces an ordered phase exhibiting a (2 x 2) LEED pattern. This pha se is a multilayer surface alloy and it has the same structure as the bulk Pt3Sn alloy. .