A van der Waals epitaxial growth of ultrathin two-dimensional Sn film on graphene covered Cu(111) substrate

Two-dimensional (2D) ultrathin gray tin (alpha-Sn) has attracted intense research efforts owing to its fascinating physical properties such as high-temperature quantum spin Hall effects, high thermoelectricity, topological superconductivity, and so on. Although monolayer alpha-Sn was achieved on substrates like Bi2Te3(111), Cu(111), Ag(111), and PbTe(111), the above-mentioned physical properties of alpha-Sn were lost due to strong Sn-substrate coupling. For promising applications of 2D Sn, it is necessary to decouple the Sn film from the substrate in order to retain the intrinsic properties of the 2D Sn film. Here, we grew ultrathin Sn films (about 6 A) on monolayer-graphene (MLG) covered Cu(111) by using molecular beam epitaxy. It was found that the van der Waals (vdW) epitaxial growth behavior was enhanced due to the template-effect of MLG, leading to the development of the 2D Sn film with a uniform thickness and continuous morphology. In addition, we also observed that the 2D Sn film on the MLG substrate is long-term stable in air. Our study provides a promising approach toward the controllable fabrication of high-quality 2D Sn films.