Isotope-engineered single-wall carbon nanotubes;: A key material for magnetic studies

Common catalysts for single-wall carbon nanotube (SWCNT) synthesis have magnetic components, even after extensive purification. This prevents their use in key experimental studies such as nuclear magnetic resonance spectroscopy and studies on the as-yet unresolved question of superconductivity and encapsulated single-molecule magnets in SWCNTs. Thus, there is a pressing need for SWCNT samples with no foreign magnetic components. Experimental spectroscopic and microscopy findings confirm that we have directly synthesized high-quality isotope-engineered SWCNTs with controllable and well-defined narrow diameter distributions. Purities better than 70% are obtained with optimization. Additionally, novel isotope effects were observed. Electron spin resonance studies explicitly show magnetization levels below the instrument limits, and superconducting quantum interference device studies show no magnetic component. The obtained SWCNTs succesfully meet a broad set of criteria, making them highly suited to a variety of important studies that will significantly advance our knowledge of SWCNTs.