Structure and Electronic Properties of Hexagonal Phosphorous Monolayer on Au(111)

Black phosphorous is a monoelemental non-planar layer material. Phosphorous atoms in each puckered layer are sp³ hybridized and stacked together by a weak van der Waals force. It possesses layer-dependent tunable bandgap properties and thus promising for optoelectronics industries. However, the controlled growth of a phosphorus monolayer remains a challenge. A large number of 2D allotropes of phosphorus have been predicted and a few of them have been realized experimentally. Among them, blue phosphorene with a honeycomb puckered structure has been reported by in-situ growth on Au(111). Phosphorus nanostructures have also been obtained in the submonolayer regime, including nanoribbons, chains, tubular structures, or hexagonal lattices. Here we present the controlled growth and electronic properties of a flat hexagonal phosphorous monolayer on Au(111). We found that the phosphorous atoms are assembled into chains, rings, porous networks, or, hexagonal monolayers depending upon the P-flux exposure duration. The lattice spacing of such structures is 5 Å, which is 1.5 times larger than that of Blue P i.e. 3.3 Å and √3 times of Au(111) lattice constant. The local spectroscopy reveals that the electronic spectrum of the phosphorus structures is different from blue phosphorus, and evolves from a featureless spectrum on small nanostructures to the formation of an electronic band on the 2D lattice including a partial flat band.