Revealing the Atomic Structure of Blue Phosphorus Phases on Au(111) with Noncontact Atomic Force Microscopy

Blue phosphorene (BlueP), a two-dimensional phosphorus allotrope with a buckled honeycomb lattice, has attracted significant interest for its semiconducting properties that extend beyond graphene. Yet, its growth on Au(111) remains debated, with structural phases highly discussed due to the possible incorporation of substrate adatoms into the phosphorus adlayer. Here, we present a general methodology combining noncontact atomic force microscopy (nc-AFM) and force spectroscopy to unambiguously discriminate between competing structural models of BlueP/Au(111) obtained by density functional theory (DFT). Each phosphorus phase is resolved at the atomic scale by nc-AFM imaging, while site-dependent force spectroscopy probes local atomic corrugations within the structure. Comparison with probe-particle simulations using DFT coordinates reveals that all structural phases on Au(111) consist of an assembly of BlueP₉ or BlueP₁₆ units stabilized by Au adatoms. These findings not only solve the long-standing debate over the phosphorus-Au(111) interface but also provide an experimental strategy for identifying atomic structures of epitaxial Xenes.