Micrometre-length continuous single-crystalline nm-thin Fe₃C-nanowires with unusual 010 preferred orientation inside radial few-wall carbon nanotube structures: the key role of sulfur in viscous boundary layer CVS of ferrocene

A key challenge in the fabrication of carbon nanotubes filled with ferromagnetic nanowires is the control of the number of nanotube-walls together with the nanowire continuity, composition and crystallinity. We report the serendipitous observation of novel radial carbon nanotube structures with few walls (2-5 walls) filled with nm-thin and many-micrometres long continuous single-crystalline Fe₃C nanowires. These are the dominant reaction products in chemical vapour synthesis experiments involving the pyrolysis of ferrocene/sulfur mixtures in the viscous boundary layer between a rough surface and a laminar Ar flow. These nanowires are found with an unusual preferred 010 orientation along the nanotube capillary. The properties of these structures are investigated through the use of multiple techniques: SEM, TEM, HRTEM, EDX, STEM, XRD, Raman spectroscopy, FT-IR spectroscopy and VSM.