Linear and Helical Cesium Iodide Atomic Chains in Ultranarrow Single-Walled Carbon Nanotubes: Impact on Optical Properties

Abstract

One-dimensional (1D) atomic chains of CsI were previously reported in double-walled carbon nanotubes with ∼0.8 nm inner diameter. Here, we demonstrate that, while 1D CsI chains form within narrow ∼0.73 nm diameter single-walled carbon nanotubes (SWCNTs), wider SWCNT tubules (∼0.8−1.1 nm) promote the formation of helical chains of CsI 2 × 1 atoms in cross-section. These CsI helices create complementary oval distortions in encapsulating SWCNTs with highly strained helices formed from strained Cs 2 I 2 parallelogram units in narrow tubes to lower strain Cs 2 I 2 units in wider tubes. The observed structural changes and charge distribution were analyzed by density-functional theory and Bader analysis. CsI chains also produce conformation-selective changes to the electronic structure and optical properties of the encapsulating tubules. The observed defects are an interesting variation from defects commonly observed in alkali halides as these are normally associated with the Schottky and Frenkel type. The energetics of CsI 2 × 1 helix formation in SWCNTs suggests how these could be controllably formed.

Zigzag HgTe Nanowires Modify the Electron–Phonon Interaction in Chirality-Refined Single-Walled Carbon Nanotubes

“… 54 After HgTe zigzag filling, however, the G-mode sideband decayed much more rapidly and was fit (dashed red line) by a single-exponential decay with lifetime τ = 0.16 ps. This faster decay may signify that HgTe filling strains the CNTs, 17 thereby boosting the anharmonic relaxation pathways for the G-mode phonons to relax into other phonons within the SWCNT. Alternatively, the presence of encapsulated insulating nanowire chains has been shown theoretically to increase hot phonon relaxation rates by providing extra phonon decay channels.…”

“…These results imply that HgTe filling may alter the higher lying electronic states in a complex manner that depends on the chirality of the SWCNT. One mechanism for this is that a zigzag chain should distort the encapsulating SWCNT’s cross-section into an oval, 17 modifying the electronic wave function. Moreover, a positive photoabsorption (PA) feature positioning at around 3.09 eV was discovered, with distinctly slower recombination than for the (7,5) and (7,6) S 33 features.…”

Applications of Pristine and Functionalized Carbon Nanotubes, Graphene, and Graphene Nanoribbons in Biomedicine

“…The technique to achieve an endohedral functionalization or simply filling of CNTs has to be chosen according to the chemical ad physical stability of the respective filler molecules or substance [42][43][44][45][46][47][48][49][50]. High-temperature processes such as the capillary filling technique can be employed for salt melts such as metal halogenides or elemental metals.…”

The Role of Temperature on the Degree of End-Closing and Filling of Single-Walled Carbon Nanotubes

“…There is a special interest in using SWCNTs as enclosures for the encapsulation of payloads [6][7][8][9]. The nanotubes offer protection to the hosted material from the external environment, thus allowing, for instance, the encapsulation of air sensitive materials [10], gases [11], and even radionuclides [12,13].…”