Epitaxial growth of monolayer white phosphorus on Cd(0001)

As a promising two-dimensional (2D) material, phosphorene has attracted tremendous research interest in both fundamental research and potential applications. Up to now, black phosphorene, blue phosphorene, violet phosphorene, and ultrathin nanosheets of red phosphorus have been successfully synthesized by mechanical exfoliation or epitaxial growth, while the synthesis of 2D white phosphorus (WP) has not been achieved. Here, we report the epitaxial growth of monolayer WP on Cd(0001) by means of low temperature (90 K) deposition. Scanning tunneling microscopy observation and first-principles calculations demonstrate that the monolayer WP is comprised of parallel dimer rows of P4 molecules, resembling the a–c plane of γ-phase WP. The monolayer WP is semiconducting with a bandgap of 1.5 eV. Increasing the substrate temperature to 120 K leads to the formation of a quasi-3 × 3 superstructure with building blocks of P4 nonamers. Voltage pulses from STM tip result in the structural transition from the quasi-3 × 3 superstructure to a 3 × 1 superstructure, of which the latter consists of alternating dimer rows and polymerized monomer rows. These observations demonstrate the essential role of dimerization, trimerization, and polymerization of P4 molecules in the formation of 2D white phosphorus.