Hybrid structures consisting of 1D crystals of C60 molecules inside single-walled nanotubes (SWNTs) "freeze" below 25K – that is, they no longer freely rotate but become rigidly aligned in one direction along the axes of the tubes. The phenomenon was observed by enriching the C60 molecules with carbon-13 and tracking their dynamics using Nuclear Magnetic Resonance (NMR), in particular High-Resolution Magic Angle Spinning Solid State NMR from room temperature down to 4K.
Until now, such NMR techniques have not been used very much to study nanostructures because the samples investigated were too impure. In contrast, the C60 peapods-SWNTs, studied by Christophe Goze-Bac of CNRS/Montpellier University in France and colleagues Edy Abou-Hamad and Younghyun Kim, were highly pure thanks to specially developed magnetic purification techniques that took a decade to perfect by the team.
The result provides a new insight into such structures and will allow researchers to further model the properties of these materials. This will ultimately help them to understand how the structures could be employed in various applications, including nano-memory devices, energy storage, nano-medicine and drug delivery. Here, local dynamics of the encapsulated molecules play a major role, says Goze-Bac. "To know more about the physics of 1D-confined molecules in general is also very interesting because confinement profoundly changes the properties of matter," he told nanotechweb.org.
The C60 peapods-SWNTs are typical of a new generation of hybrid nanostructured materials and the team now plans to further investigate their magnetic and electronic properties, as well as applications in NMR imaging.
"This work was only possible by exchanging people, knowledge and materials between groups in Montpellier for the NMR spectroscopy, Berkeley, Philadelphia (US) and Umea (Sweden) for the materials science, and San Sebastian (Spain) for the theory part," added Goze-Bac. "Nanotechnology is interdisciplinary and needs such collaborations."
The work was published in ACS Nano.