Epitaxial growth of two-dimensional Pb and Sn films on Al(111)

Single and binary two-dimensional (2D) films of Pb and Sn on Al(111) at room temperature were investigated using low-energy electron diffraction (LEED) and scanning tunneling microscopy. The 2D Pb and Sn films form a (√ 31 × √ 31)-Pb structure with close-packed six-fold symmetry and a (“2” × √ 3)-Sn structure with square-like fourfold symmetry, respectively. The 2D bimetallic Pb-Sn films only exhibit (√ 31 × √ 31)-Pb and/or (“2” × √ 3)-Sn LEED patterns in any compositional ratio of Pb to Sn. Sub-monolayer Sn deposition on the 2D Pb film reveals (“2” × √ 3)-Sn LEED pattern, indicating the preferential formation of the 2D Sn film. These results indicate that monolayer Pb and Sn films are immiscible on Al(111).