Microstructural constructing 2D tin allotropes on Al(111): from quasi-periodic lattice to square-like lattice

The lattice arrangement and degree of buckling have been playing vital roles in the structure stability, bonding configuration, and electronic band structures of two-dimensional (2D) single-layer materials. Here, we fabricate two tin allotropes beyond honeycomb stanene by epitaxial growth method on Al(111). Sn-I phase with quasi-periodic lattice and Sn-II phase with square-like lattice have been identified by scanning tunneling microscopy. Combined with scanning tunneling spectroscopy, it is revealed that Sn-II phase with four-coordinate tin atoms exhibits enhanced decoupling effects due to their saturated bonds. In this study, the discovery of new lattice arrangements with well-defined atomic structures beyond honeycomb lattice provides an appealing approach to searching 2D elemental single layers and novel physical properties.