High filling of single wall carbon nanotubes (SWCNT) with C60 and C70 fullerenes in solvent is reported at temperatures as low as 69 o C. A 2 hour long refluxing in n-hexane of the mixture of the fullerene and SWCNT results in a high yield of C60,C70@SWCNT, fullerene peapod, material. The peapod filling is characterized by TEM, Raman and electron energy loss spectroscopy and X-ray scattering. We applied the method to synthesize the temperature sensitive (N@C60:C60)@SWCNT as proved by electron spin resonance spectroscopy. The solvent prepared peapod samples can be transformed to double walled nanotubes enabling a high yield and industrially scalable production of DWCNT.

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.

C59N magnetic fullerenes were formed inside single-wall carbon nanotubes by vacuum annealing functionalized C59N molecules encapsulated inside the tubes. A hindered, anisotropic rotation of C59N was deduced from the temperature dependence of the electron spin resonance spectra near room temperature. Shortening of spin-lattice relaxation time, T1, of C59N indicates a reversible charge transfer toward the host nanotubes above ∼ 350 K. Bound C59N-C60 heterodimers are formed at lower temperatures when C60 is co-encapsulated with the functionalized C59N. In the 10-300 K range, T1 of the heterodimer shows a relaxation dominated by the conduction electrons on the nanotubes.Single-wall carbon nanotubes (SWCNTs) [1, 2] exhibit a variety of unusual physical phenomena related to their one-dimensional and strongly correlated electronic properties. These include excitonic effects [3,4], superconductivity [5], the Tomonaga-Luttinger liquid state [6], and the Peierls transition [7]. Magnetic resonance is a powerful method to study strong correlations in low dimensional systems. However, for SWCNTs both nuclear magnetic resonance (NMR) and electron spin resonance (ESR) are severely limited by NMR active 13 C nuclei and ESR active electron spins in residual magnetic catalytic particles and other carbon phases. Synthesis of 13 C isotope engineered SWCNTs solved the problem for NMR [8,9]. To enable ESR spectroscopy of SWCNTs, a local probe, specifically attached to SWCNTs, is required. The N@C 60 [10] and C 59 N [11] magnetic fullerenes are ideal candidates for such studies. In fullerene doped SWCNTs, fullerenes occupy preferentially the interior of the tubes and form "peapods" (C 60 @SWCNT) [12]. Fullerenes adhesing to the outside can be removed [13] in contrast to e.g. filling with iron [14]. ESR on encapsulated magnetic fullerenes could yield information on the electronic state of the tubes and it could also enable to study the fullerene rotational dynamics in a confined environment. In addition, magnetic fullerene peapods could exploit the combination of the SWCNT strength and the magnetic moment of molecules in magnetic scanning probe tips and they could enable a bottom-up design for magnetic storage devices or for building elements of quantum computers [15].Typical spin concentrations in (N@C 60 :C 60 )@SWCNT are low, ∼1 spin/tube, and the N spins are insensitive to SWCNT properties [16]. The C 59 N monomer radical is a better local probe candidate as the unpaired electron is on the cage. C 59 N can be chemically prepared but it forms spinless dimers (C 59 N) 2 or monomer adducts [11].The magnetic C 59 N monomer radical can be stabilized as C 59 N:C 60 , a dilute solid solution of C 59 N in C 60 [17].Here, we report on the first ESR study of SWCNT properties and peapod rotational dynamics using a paramagnetic local probe: C 59 N monomer radicals encapsulated inside SWCNTs. SWCNTs were first filled with chemically inert C 59 N derivatives. A heat treatment in vacuum removes the side-group and the monomer radical is left behin...