Structure and dynamics of carbon buckyballs encapsulated into Single-Walled carbon Nanotubes
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Structure and dynamics of carbon buckyballs encapsulated into Single-Walled carbon Nanotubes Julien Cambedouzou, Stéphane Rols, Robert Almairac and Jean-Louis Sauvajol, Groupe de Dynamique des Phases Condensées (UMR CNRS 5581), Université Montpellier II, F-34095 Montpellier Cedex 5, France. H. Kataura, Nanotechnology Research Institute, National Institute of Advanced Industrial Science and Technology Central 4, Higashi 1-1-1, Tsukuba, Ibaraki 305-8562, Japan. H. Schober, Institut Laue Langevin, F-38042 Grenoble, France.
ABSTRACT The structural and dynamical properties of C60 chains inserted inside Single Walled carbon Nanotubes (SWNT) have been investigated by x-ray and neutron diffraction, and inelastic neutron scattering (INS). The measurements have been performed on a large mass of a very high quality carbon peapods sample. We showed that powder diffraction could hardly give definitive response on the way the C60s are bonded inside SWNT. However, the comparison of the neutron-derived generalized density of states (GDOS) of the inserted C60 peas with the GDOS of the same objects derived from lattice dynamics calculations led to unambiguous results. The observation of excitations in the 8-15 meV range is a clear evidence for the presence strong bonds between C60s in the sample. In the same time, the observation of a very weak quasielastic signal may be related to rotational motions of C60 monomers inside the SWNT. These results suggest that peapods are made of a mixed phase of C60 monomers and C60 n-mers. INTRODUCTION Since their first observation in 1991, single-wall carbon nanotubes (SWNT) have inspired remarkable advances in science and engineering at the nanometer scale during the past decade. Due to their size and geometry, SWNT provide a unique opportunity for nanoscale engineering of novel one-dimensional materials created by self-assembly of atoms or molecules inside the SWNT’s hollow core. Recently, SWNT encapsulating fullerenes -the so-called peapods- have been successfully synthesized [1]. Peapods are interesting materials as new solid phase of pure carbon constructed by zero (fullerene) and one-dimensional (nanotube) sp2 network. Furthermore, peapods are predicted to exhibit superconductivity properties upon alkaline doping [2]. Both structural and vibrational studies have been devoted to peapods. Transmission electron microscopy (TEM) images[1] have first shown the quasi 1D chains formed by C60 inside SWNT. Then, Raman studies have been carried out [3], and no definitive clear results were reported about the structural organization of the C60s inside SWNT. The photopolymerization of C60s under a 488 nm laser excitation has been evidenced, suggesting that the C60s are freely spinning inside SWNT at room temperature. Besides, a Raman experiment has been performed at Helium temperature to get rid of C60 photopolymerization, and then the spectra were indeed found to be stable. However, the observation of a mode at 90 cm-1, close to the frequency of the so-called Einstein dumbbells mode (96 cm-1),
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