Evolution of Low-Dimensional Phosphorus Allotropes on Ag(111)

Elemental two-dimensional (2D) materials exhibiting intriguing properties have great potential applications in next-generation electronics. However, controlling single-phase synthesis might be challenging due to the existence of various allotropes with comparable stability. Here, low-dimensional phosphorus (P) is used as a prototype for the understanding of the competition among a series of 0D-2D allotropes upon adsorption. With a combination of theoretical calculations and scanning tunneling microscopy, we find that the formation of P allotropes significantly depends on the bond angle, coordination number, and atomic density. As a result, P atoms tend to form black phosphorene (BP)-like chains and pentamer molecules at low atomic density and 2D buckling blue phosphorene at high density. In particular, a trigonal nanoribbon-like phase is observed with the confinement of the BP-like chains. The comprehensive understanding of the evolution of the elemental allotropes in low dimension could provide fundamental guidance for the construction of polymorphic quantum materials with novel functionalities.