One-Dimensional Pnictogen Allotropes inside Single-Wall Carbon Nanotubes

The discovery of phosphorene, a single layer of black phosphorus, has accelerated the investigation of pnictogen nanomaterials, leading to the recent identification of arsenene and antimonene. These two-dimensional nanomaterials display physical properties superior to those of graphene for some applications. Recently, single-wall carbon nanotubes (SWCNTs) have been filled with P4 molecules from the melt and As4 molecules from the vapor phase. Confined within SWCNTs, polymerization reactions yielded new one-dimensional pnictogen allotropes. Here, we show using high-resolution electron microscopy that such nanostructures can also be observed upon filling SWCNTs from the vapor phase using red phosphorus as the source material. Using larger-diameter SWCNTs, the vapor phase favors the formation of double-stranded phosphorus zigzag ladders observed here for the first time. Overall, however, SWCNTs were generally found to fill more efficiently with liquid phosphorus; substantial decreases in the filling yields w...