One-dimensional pnictogen allotropes inside single- wall carbon nanotubes Martin Hart,1 Ji Chen,2 Angelos Michaelides,3 Andrea Sella,1 Milo S. P. Shaffer4 and Christoph G. Salzmann*1 1 Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, United Kingdom 2 School of Physics, Peking University, Beijing 100871, P. R. China 3 Thomas Young Centre, Department of Physics and Astronomy, and London Centre for Nanotechnology, University College London, Gower Street, London, WC1E 6BT, United Kingdom 4 Department of Chemistry, Imperial College London, Imperial College Road, London, SW7 2AZ, United Kingdom E-mail:
[email protected] 1 ABSTRACT The discovery of phosphorene, a single layer of black phosphorus, has kick-started tremendous research efforts investigating the pnictogen nanomaterials. Arsenene and antimonene have now also been identified and these two-dimensional nanomaterials display physical properties superior to 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. Inside the confinement of the SWCNTs, polymerization reactions were observed yielding 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 and filling from the vapor phase favors the formation of double-stranded phosphorus zig-zag ladders observed here for the first time. SWCNTs were generally found to fill well with liquid phosphorus. However, substantial decreases in the filling yields were observed for both phosphorus and arsenic filling of narrow SWCNTs using the vapor route.