Nucleation of carbon-sulfur phases by manipulation of vertically-aligned mm-long films of iron-filled few-wall/multiwall carbon nanotubes

•We report a novel Cl- & S-assisted fabrication of vertically-aligned mm-long films of few-walls carbon nanotubes (CNTs).•The employed quantity of sulfur was found to yield either few wall CNTs (FWCNTs) or multiwall CNTs (MWCNTs) in presence of 0.4 mg or 1.2 mg.•Structural manipulation was sought through annealing at T∼ 150 °C, 300 °C and 600 °C in presence of high concentration of sulfur.•We demonstrate the appearance of dominant Raman bands indicative of carbon-sulfur bonding (shifts of 1250 cm−1 and 1450 cm−1) at T∼ 150  °C, 300 °C.•The effects of the doping process were investigated through T-dependent EPR.