While various electronic components based on carbon nanotubes (CNTs) have already been demonstrated, the realization of miniature electromagnetic coils based on CNTs remains a challenge. Coils made of single-wall CNTs with accessible ends for contacting have been recently demonstrated but were found unsuitable to act as electromagnetic coils because of electrical shorting between their turns. Coils made of a few-wall CNT could in principle allow an insulated flow of current and thus be potential candidates for realizing CNT-based electromagnetic coils. However, no such CNT structure has been produced so far. Here, we demonstrate the formation of few-wall CNT coils and characterize their structural, optical, vibrational, and electrical properties using experimental and computational tools. The coils are made of CNTs with 2, 3, or 4 walls. They have accessible ends for electrical contacts and low defect densities. The coil diameters are on the order of one micron, like those of single-wall CNT coils, despite the higher rigidity of few-wall CNTs. Coils with as many as 163 turns were found, with their turns organized in a rippled raft configuration. These coils are promising candidates for a variety of miniature devices based on electromagnetic coils, such as electromagnets, inductors, transformers, and motors. Being chirally and enantiomerically pure few-wall CNT bundles, they are also ideal for fundamental studies of interwall coupling and superconductivity in CNTs.
Keywords: Raman; carbon nanotubes; coil; molecular dynamics; multiwall carbon nanotubes; self-organization; transmission electron microscope.