Metastable and equilibrium structures onPt3Sn(001)studied by STM, RHEED, LEED, and AES

After sputtering and moderate annealing (600 K) the ${\mathrm{Pt}}_3\mathrm{Sn}\mathrm{}\left(001\right)\mathrm{}$ surface shows a $c(2\mathrm{}\times 2)$-LEED pattern with streaky facet spots. The scanning tunneling microscopy (STM) images show pyramidal features that mainly consist of (102) facets, in addition to flat parts between and on top of the pyramids. On the flat parts the dominating feature are triple atomic rows, which probably consist of Pt. According to Auger electron spectroscopy the Sn surface concentration is reduced due to preferential sputtering. Annealing at 1000 K restores the Sn surface concentration and leads to an improved $c(2\mathrm{}\times 2)$-LEED pattern with no facet spots. With the STM the disappearance of the pyramids and the formation of large flat terraces with added single atomic rows along the [100] and [010] surface directions is observed. All steps found are double steps, indicating a strict termination with the mixed Pt/Sn layer. Chemical contrast between Pt and Sn atoms is observed.