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 (root 31 x root 31)-Pb structure with close-packed six-fold symmetry and a ("2" x root 3)-Sn structure with square-like fourfold symmetry, respectively. The 2D bimetallic Pb-Sn films only exhibit (root 31 x root 31)-Pb and/or ("2" x root 3)-Sn LEED patterns in any compositional ratio of Pb to Sn. Sub-monolayer Sn deposition on the 2D Pb film reveals ("2" x root 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). (C) 2016 Elsevier B.V. All rights reserved.