In-plane strain-free stanene on a Pd2Sn(111) surface alloy

Here we report the growth of laterally strain-free stanene, that is a two-dimensional (2D) honeycomb structure of tin atoms, on a Pd(111) crystal terminated by a Pd2Sn surface alloy. The atomic geometry and the electronic structure have been thoroughly investigated by scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), Auger electron spectroscopy, high-resolution synchrotron radiation photoemission spectroscopy, and advanced first principles calculations. The STM images clearly reveal the epitaxial growth of honeycomb stanene on the preformed Pd2Sn surface alloy. LEED patterns clearly show commensurate (root 3x root 3)R30 degrees spots, corresponding to a lattice constant of 0.47 nm, in perfect accord with the cell size of free-standing stanene. The measured very low buckling, within 20 pm, is derived from section profiles of atomic-scale STM images. This contrasts the significantly larger buckling of free-standing stanene, possibly due to a STM tip effect as well as a non-negligible interaction with the underlying surface alloy. The electronic structure exhibits a characteristic 2D band with parabolic dispersion, which is in good accordance with electronic structure calculations in density functional theory.