Large-scale synthesis of rings of bundled single-walled carbon nanotubes by floating chemical vapor deposition

The synthesis of single-walled carbon nanotubes (SWNTs) rings was performed by thermally decomposing acetylene at 1100°C in a floating iron catalyst system. The rings have a small average diameter with a narrow size distribution and consist of SWNT toroids. The Raman spectra and electrical properties of the rings have been measured. The rings can be deposited on different substrates with varying densities at relatively low temperatures, which is beneficial for applications such as electronic devices. This low-temperature deposition process allows for the integration of the rings with silicon and microelectromechanical systems technology. Energy dispersive X-ray (EDX) spectroscopy shows that the nanoparticles in the rings are iron catalysts encapsulated by several graphite layers. The cross section of the ring was observed when the plane of the ring is parallel to the incident electron beam, which shows that SWNTs with diameters of 1 to 2 mm are tightly packed within the rings.