New Phosphorene Allotropes Containing Ridges with 2- and 4-Coordination

In all of the phosphorus monolayers reported to date, phosphorus is 3-fold coordinated. However, flexible chemistry of phosphorus allows it to have varying coordination number up to 6. Here, we report three new phosphorus monolayers (labeled α-P₆, β-P₆, and 558-P₆) having 2-, 3-, and 4-fold coordination, which can be observed in epitaxial growth where flakes merge forming ridges at the boundaries. On the basis of state-of-the-art theoretical simulations, we show that these three new monolayer allotropes are thermally and dynamically stable, and they have comparable energetic stability with some reported monolayers such as δ-P, γ-P, and ε-P. Because of their special atomic configurations, they exhibit exceptional properties, including extremely high electron mobility, anisotropic Young's moduli, and optical absorbance in visible and ultraviolet regions. These findings can extend the family of phosphorenes with novel properties and potential for applications.