Structure of sulfur chains encapsulated in single-walled carbon nanotubes

The encapsulation of sulfur (S) within single-walled carbon nanotubes (S@SWCNTs) provides a unique opportunity to stabilize and study the structure and bonding of one-dimensional sulfur chains, which do not exist in a free state. In this work, we present a detailed structural investigation of S@SWCNTs using temperature-dependent x-ray absorption fine structure spectroscopy. The S-S covalent bond length was 2.057 ± 0.004 Å, which is identical to that of bulk<i>α</i>-S within the experimental uncertainty. Crucially, both the bond length and its mean-square relative displacement exhibited no discernible temperature dependence up to 300 K, indicating an exceptionally robust covalent bond. Comparison between the experimental and theoretical x-ray absorption near edge structure spectra suggested that the possible chain conformations are zigzag and linear, rather than three-turn helical. Photoemission spectroscopy measurements revealed that the C 1s core level binding energy did not change upon sulfur encapsulation, confirming the absence of interaction between the sulfur chains and the host SWCNTs.