Abstract
Two-dimensional (2D) materials have attracted lots of research attention in the past decade because of their extraordinary electronic and optoelectronic properties as well as potential device applications. Transition-metal dichalcogenides (TMDs) are a genre of 2D materials that cover a wide range of properties. Some TMDs even exhibit non-trivial characters as superconductors, topological insulators, etc. Layered phosphorus is a late but important member in the 2D material family. Single- or few-layer black phosphorus has been widely studied recently. Besides black phosphorus, there are also other layered phosphorus allotropes being proposed and experimentally realized. Blue phosphorus is one of the most attractive allotropes, who is predicted to be as stable as black phosphorus and shows comparable electronic and optical properties.
Three new 2D systems are studied by scanning tunneling microscopy (STM). The first is blue phosphorene grown on Au(111). Reports have shown that a (4 × 4)-reconstructed blue phosphorene can be stabilized on a (5 × 5)-cell of Au(111) surface. We find a particular coverage jump of phosphorus in the growth process. It indicates the existence of an interesting mechanism of surface dewetting accompanied by the phase separation.
The second system is the layered phosphorus grown on Pt(111). As a noble metal, Pt(111) surface can also capture the reactive phosphorus atoms. We find that depending on phosphorus coverage and growth temperature, phosphorus can form five kinds of superstructures on Pt(111) surface. The structural and electronic properties of these superstructures are characterized by STM. The possible links between these structures are proposed.
The final system is MoTex (x ~ 1.6) that emerged in growing monolayer MoTe2 due to the creation of a dense network of twin domain boundary defects. Indeed, when the twin domain boundaries become super-dense and regularly arranged, the film no longer exhibits properties of the 1D defects or that of intrinsic MoTe2. Our experiments confirmed the existence of the MoTe1.6 and that it can stably co-exist with the 1H and 1T’ phases of MoTe2.