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We present low-temperature heat capacity measurements performed on two different kinds of single-walled carbon nanotube bundles which essentially differ in their mean number of tubes (NT) per bundle. For temperatures below a few kelvin, the vibrational heat capacity can be analysed as the sum of two contributions. The first one is a regular T3 phononic one, characteristic of the three-dimensional (3D) elastic character of the bundle for long-wavelength phonons. A crossover to a lower effective dimensionality appears at a few kelvin. From the 3D contribution, we estimate a mean sound velocity, and hence a mean shear modulus of the bundle. The difference in amplitude of the acoustic term and in the crossover temperature between the two samples is ascribed to the different bundle topology (i.e. NT). The second contribution, of similar amplitude in both kinds of samples, shows a peculiar power law Ta variation (a $<$ 1) indicative of localized excitations, very probably due to intrinsic structural defects of the nanotubes.

@article{ title = {Low-energy vibrational excitations in carbon nanotubes studied by heat capacity}, type = {article}, year = {2003}, identifiers = {[object Object]}, pages = {998-1003}, volume = {14}, websites = {http://stacks.iop.org/0957-4484/14/998}, id = {02e27fb5-246c-33c2-bba3-0f178a5db884}, created = {2016-12-15T10:02:46.000Z}, file_attached = {false}, profile_id = {12182ba0-f80b-33ff-8da5-1813b38b682d}, group_id = {60cbc7ed-7d3c-385a-96b0-5920f1dfe2f9}, last_modified = {2016-12-21T14:16:38.000Z}, read = {false}, starred = {false}, authored = {false}, confirmed = {true}, hidden = {false}, citation_key = {Lasjaunias2003b}, abstract = {We present low-temperature heat capacity measurements performed on two different kinds of single-walled carbon nanotube bundles which essentially differ in their mean number of tubes (NT) per bundle. For temperatures below a few kelvin, the vibrational heat capacity can be analysed as the sum of two contributions. The first one is a regular T3 phononic one, characteristic of the three-dimensional (3D) elastic character of the bundle for long-wavelength phonons. A crossover to a lower effective dimensionality appears at a few kelvin. From the 3D contribution, we estimate a mean sound velocity, and hence a mean shear modulus of the bundle. The difference in amplitude of the acoustic term and in the crossover temperature between the two samples is ascribed to the different bundle topology (i.e. NT). The second contribution, of similar amplitude in both kinds of samples, shows a peculiar power law Ta variation (a $<$ 1) indicative of localized excitations, very probably due to intrinsic structural defects of the nanotubes.}, bibtype = {article}, author = {Lasjaunias, K Biljakovic J C and Sauvajol, J L}, journal = {Nanotechnology}, number = {9} }

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