“Missing” One-Dimensional Red-Phosphorus Chains Encapsulated within Single-Walled Carbon Nanotubes

Abstract

We identify the “missing” 1D-phosphorus allotrope, red phosphorus chains, formed in the interior of tip-opened single-walled carbon nanotubes (SWCNTs). Via a comprehensive experimental and theoretical study we show that in intermediate diameter cavities (1.6–2.9 nm), phosphorus vapor condenses into linear P8]­P2 chains and fibrous red-phosphorus type cross-linked double-chains. Thermogravimetric and X-ray photoelectron spectroscopy analysis estimates ∼7 atom % of elemental phosphorus in the sample, while high-resolution energy dispersive X-ray spectroscopy mapping reveals that phosphorus fills the SWCNTs. High-resolution transmission electron microscopy (HRTEM) shows long chains inside the nanotubes with varying arrangement and packing density. A detailed match is obtained between density functional theory (DFT) simulations, HRTEM, and low-frequency Raman spectroscopy. Notably, a signature spectroscopic signal for phosphorus chain cross-linking is identified. When coupled with reinterpretation of literature data and wide-ranging DFT calculations, these results reveal a comprehensive picture of the diameter dependence of confined 1D-phosphorus allotropes.

Doping of Carbon Nanotubes with Encapsulated Phosphorus Chains

“…According to DFT calculations, the first peak corresponds to the bending mode, while the higher-frequency peaks are associated with symmetric stretching modes of the P 4 tetrahedron . The Raman spectrum of the red phosphorus sample has a shape characteristic of amorphous forms of red phosphorus. , A set of low-intensity peaks in the region from 200 to ∼320 cm –1 corresponds to oscillations of the eight-membered P 8 cage, and a wide band between 320 and 490 cm –1 is due to P–P stretching modes in chain structures containing P 8 and P 9 cages . These cages are considered as the basic building units of amorphous red phosphorus .…”

“…The appearance of single, double, and triple chains in the P@SWCNTs_800 sample is associated with different diameters of host nanotubes (Figure e). The change in the phosphorus pattern along the same SWCNT (shown by the corner arrow in Figure c) could be due to the imperfections in the chain structures or their rotation inside the SWCNT under the electron beam …”

“…Phosphorus vapor pressure increases at higher synthesis temperatures, which leads to more efficient filling of SWCNTs. The large diameters of the SWCNTs used favor the formation of bundles of phosphorus chains …”

One-Dimensional Atomic Chains for Ultimate-Scaled Electronics

“…On the other hand, elemental RP possesses a bandgap of 1.69 eV, close to iodine-based perovskites, which has the potential for achieving low-cost light absorption components (Figure b). Lately, 1D RP ACs were encapsulated within conductive and robust single-walled CNTs, by which their applications in ion batteries, supercapacitors, and photocatalysis were highlighted …”

“…Lately, 1D RP ACs were encapsulated within conductive and robust singlewalled CNTs, by which their applications in ion batteries, supercapacitors, and photocatalysis were highlighted. 70 In complementary technologies, extrinsic doping processes, such as ion implantation and thermal diffusion, are generally used to obtain p-type or n-type unipolar semiconductors. Besides, some exceptional cases of CNTs, layered 2D materials, and organic semiconductors could show ambipolar characteristics, as the concentrations of the electron and hole carriers are comparable.…”