Collapse of G⁺/G^- bands, modification of Breit–Wigner–Fano signals and structural amorphization in single wall carbon nanotube networks under great excess of sulfur

The identification of superconductivity and ferromagnetic to superconductive transitions in sulfur-modified carbons has recently attracted an important attention. Additional work is however needed to better understand the structural modification of the graphitic interfaces in presence of sulfur. Here we report on an advanced methodology which involves soaking of large amounts (in the order of 500 mg) of sulfur through several annealing cycles into bundles comprising of hollow single-wall/few-wall carbon nanotubes (SWCNTs). TEM, HRTEM, XRD and Raman spectroscopy characterization analyses reveal the presence of structural amorphization of the SWCNTs, with dramatic impact on the intensity of the G⁺ and a progressive vanishing of the G^- signal-contribution. We demonstrate the presence of high sulfur content by employing both point and mapping energy dispersive X-rays (EDX maps) acquisitions, with high local quantities of sulfur in the order of 16 %. Interestingly, a complex variation in the contribution of the Breit-Wigner-Fano (BWF) band, with appearance of extra D, G⁺ and C-S band-contributions, is revealed by deconvolution-analyses. The appearance of these structural features is a clear indicator of structural amorphization of the CNTs, with consequential formation of C-S hybrid structures, which we analyze systematically with the aid of energy dispersive X-ray spectrum mapping and Raman point/mapping spectroscopy approaches.