Structural and microstructural study of novel stacked toroidal carbon nanotubes

The work presents a new carbon nanostructure in the form of stacked toroidal carbon nanotubes (STCNT) crystallized from the gas phase through a catalyst-free deposition process. Vapor-grown STCNT were obtained on a graphite substrate using methane as a source of carbon. The carbon structure was analyzed using Transmission Electron Microscopy (TEM), Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM/EDX), Raman spectroscopy, X-ray Diffraction and X-ray photoelectron spectroscopy. The TEM images revealed that the nanostructured carbon phase consisted of a single toroidal element (toroid) that was composed of rolled multi-walled carbon nanotubes. The SEM/EDX study of different substrate sites showed the presence of the pure carbon structure. The average external diameter of a single toroid was 1000 nm, and the average distance between neighboring toroids was 100 nm. The space inside the toroids contained carbon spheres made of turbostratic crystallites.