Atomic adsorption of Sn on mechanically cleaved WS2 surface at room temperature

Abstract

Room temperature (RT) adsorption of tin (Sn) under ultra-high vacuum (UHV) conditions on mechanically cleaved tungsten disulfide (WS2) surfaces is reported here. In-situ low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) studies indicate commensurate adsorption of Sn on the hexagonal surface of WS2. Bare WS2 displays an atomic periodicity of lattice constant 0.34 nm. Growth of Sn reveals monomer like a single atom or unpaired (U) and dimer like- or paired (P) adsorptions on the top (`T’) sulfur (S) sites of the trigonal prismatic sublattice within the honeycomb lattice of WS2. The lateral distance between two nearest adsorbed monomers is around 0.34 nm which is exactly similar to the atomic periodicity of the underneath WS2 substrate crystal. For the case of dimer like- adsorption, the separation between two adspecies is 0.293 nm. The bond length of the adsorbed Sn with the surface S atoms is around 40 (±10) pm. We do not find any evidence of Sn adsorption on the bridge (`B’) or hollow (`H’) site of the WS2 lattice. Analysis of the LEED spots and the FFT images of the STM micrographs after Sn adsorption discloses a stretched hexagonal surface which is most likely due to the overall consequence of a perfectly commensurate monomer and nearly commensurate dimer like- adsorptions of the Sn atoms on the WS2 surface.