Low-energy vibrational excitations in carbon nanotubes studied by heat capacity (CROSBI ID 100561)
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Lasjaunias, Jean Claude ; Biljaković, Katica ; Monceau, Pierre ; Sauvajol, Jean Louis
engleski
Low-energy vibrational excitations in carbon nanotubes studied by heat capacity
We present low temperature heat capacity measurements performed on two different kinds of single-walled carbon nanotube (SWNT) bundles, which essentially differ by 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 3 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 T*alpha variation (alpha<1) indicative of localized excitations and it is very probably due to intrinsic structural defects of the nanotubes.
Thermal properties; nanotubes; phonons or vibrational states; disordered systems
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