Neutron Spectroscopy of Carbon nano-Materials
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Neutron Spectroscopy of Carbon nano-Materials Alexander I. Kolesnikov1, Chun-K. Loong1, Alexander P. Moravsky2, Raouf O. Loutfy2, and Christian J. Burnham3 1 Argonne National Laboratory, Intense Pulsed Neutron Source Division, 9700 South Cass Avenue, Argonne, IL 60439 2 MER Corporation, 7960 South Kolb Road, Tucson, AZ 85706, USA 3 Henry Eyring Center for Theoretical Chemistry, University of Utah, Salt Lake City, Utah, 84112-0850, USA. ABSTRACT Vibrational spectra for single wall carbon nanotubes, double wall carbon nanotubes, single wall carbon nanohorns and C60-peapods have been measured with inelastic neutron scattering in a wide range of energy transfer, 5-220 meV. A decrease in intensity around 75-100 meV and the appearance of two peaks around 120-125 meV and 150 meV in the double wall nanotubes and C60-peapods spectra compared to single wall carbon nanotubes and nanohorns were observed. These findings indicate the possibility of strong interaction between the walls of the double wall carbon nanotube, and between C60 molecules and carbon nanotube of the peapod. Alternatively, a possible contamination of the samples by hydrogen (even in microscopic quantities) covalently bonded to the carbon also can account for the observed phenomena. INTRODUCTION Although the existence of varieties of carbon nano-materials has been known for some time, the investigation of their vibrational spectra has been limited mainly to the use of optical spectroscopy. In spite of the well-recognized advantages of inelastic neutron scattering (INS) technique, namely, unrestricted by the selection rules of infrared and Raman spectroscopy and accessible to all vibrational modes in the reciprocal space, so far this method was used for the study of only fullerens (see e.g. review in [1]) and single-walled carbon nanotubes (SWNT) [2,3]. Here we present the INS measurements on a series of carbon nano-materials: SWNT, double-walled carbon nanotubes (DWNT), single wall carbon nanohorns (SWNH), and fullerene-C60 encapsulated into SWNT (so called C60-peapods), aiming at the characterization of the vibrational spectra over a wide energy scale (up to 220 meV) for this family of related materials.
EXPERIMENTAL DETAILS AND SAMPLE CHARACTERISATION The high-quality samples of SWNT (3.8 g, ~14 Å diameter)), DWNT (1.3 g, ~25 Å outer diameter), C60-peapods (3.3 g, ~15 Å diameter of nanotube) and SWNH (14.2 g, ~25 Å diameter) were prepared by MER using methods described elsewhere (see e.g. [4-6]). The high purity and the narrow variation of the nanotube diameters were quantified by transmission electron microscopy (TEM), neutron diffraction (ND) and Raman (for SWNT) measurements. The well-known hexagonal packing of the carbon nanotubes into bundles are clearly seen in TEM pictures (figure 1, at the top) and were used for tube size characterization. ND patterns of
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the samples show a peak at small momentum transfer, Q, due a Bragg reflection in the structure factor S(Q) from the (01) planes of the two-dimensional hexagonal lattice of the cry
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