2D self-assembly of phosphorus allotropes on Bi(111)

Phosphorus allotropes have attracted extensive interest in both fundamental research and potential applications. As the basic units of white P, tetrahedral P4 molecules have been the subject of extensive investigation. Here, we report the formation of self-assembled monolayers and the second layers of P4 molecules on a Bi(111) surface. At the initial adsorption stage, P4 molecules form a self-assembled monolayer that is commensurate with the Bi(111) substrate, adopting a √13 × √13 superstructure. The building blocks of this monolayer are P4 nonamers arranged in a clover-like motif. Further deposition leads to the formation of the second layer of P4 with a 2√3 × 2√3 superstructure. Scanning tunneling spectroscopy measurements reveal that the P4 monolayer has a bandgap of 1.55 eV, smaller than the gap (1.69 eV) of the second layer.